As you might expect, the setup time is designed for the defending team (particularly medics and engineers) to set up defences and prepare for the attack.
Therefore there isn't really much for the offensive team to do other than build Uber and do the conga, but you can always use the time to communicate with your team to plan attacking strategy.
Heavies can even throw down a hidden sandwich for quick health regen on maps where the resupply lockers are far from the gates.
Otherwise popular activities include taunting, repeatedly hitting a teammate with the frying pan, or rocket jumping aimlessly until the time ticks down.
gaming.stackexchange.com/users/41423/imulsion
There are many small things that can be done, but Medics building Uber is probably the most useful thing that can be done while on offense.
On some maps, engineers on the offensive team can also begin building up their buildings.
Depending on your level of play, you can attempt to see where some of the enemies are setting up
so you know which chokepoints to use and not use at the start of the match.
A heavy with the dalokahs bar or a scout with the bonk can use it before the gates open at the optimal time to have its effects ready for the match to start.
A pyro could light a huntsman arrow on fire for a sniper should they wanna.
A demo could place a sticky trap by their own gates in case the enemy also placed some stickies down or want to hang out and try to spawn camp.
A spy with the cloak and dagger may want to be cloaked well before the match starts if they wanna try to find a safe place to hide at without the enemies knowing for sure that there is a spy on the offensive team.
If it's not so serious, taunting is also an option, among a quick trade, or even use the time to check on something in real life.
gaming.stackexchange.com/users/173448/WaveX
You can jarate people through the gate if they come close enough.
If you have a friend, you can have them damage themselves with the Boston Basher or explosive weapons, and then feed them sandviches for bonus points.
On some maps you can build as an engineer.
(On Gravelpit.
You used to able to build a sentry in Badwater spawn, but they patched that, but maybe there are others)
gaming.stackexchange.com/users/207169/user207169
There's plenty to do while waiting in spawn.
Here's what I generally try to do: 1.
(Attempt to) Communicate with teammates
Say
Hi.
Ask how their day is going.
Establish a rapport, then (in conjunction with point #4) work out some game plan with them (Heavy+Med to exit right door, Bonk scout to distract sentry, and so on).
This won't always work of course - some people just don't communicate, or aren't interested.
That's the nature of pubs.
But you won't know unless you try.
2.
Keep an eye on your team's class composition Look around at your teammates spawning in, and occasionally check the 'class change' screen.
Do you notice a distinct lack of Power classes?
Is your team lacking a Medic?
Are there 5 Snipers?
Consider switching to what your team is lacking, and ask others to do the same* (easier to do if you've established a rapport, see #1).
Also have a look at your loadouts, and ensure that they're what you want to use for the upcoming match.
*
It's easier to convince others to switch if you give them a reason to do so: "
Hey, if one of the Snipers wants to go Heavy, I'll Uber you out the left door and we can smash up their Sentry Nest.
" is a lot more appealing than "OMG can we not have 5 Snipers?" 3.
(Medic) Build Overheal and Ubercharge Thanks!
You've picked Medic!
You know what to do.
Build up your teammate's Overheal as well as your own Ubercharge.
Then - just like the peacock - find a mate with the flashiest hats* and Uber him out the gate.
* Not always a guarantee that this person is a good player.
In all seriousness, I'm assuming you know the basics of how to play Medic.
If not, start here .
4.
Peek out the gate at the other team Check the other team's composition:
Do they have 3 Engies setting up a nest on the right side?
Are 4 Snipers scoped in on the middle door?
Are Demomen laying sticky traps at the gates/choke/cart/point?
Are Pyros getting into position to roast people as they leave spawn?
Is one or more of your teammates wandering around outside with the enemy team?
(If so, Press X + 2 ) Use this info in conjunction with #1 to formulate game plans with your team.
5.
Help your Engie level up buildings On some maps, it's possible to build inside the spawn area.
If an Engineer is trying to get a Dispenser or Sentry to Level 3, switch over to Engie and whack his buildings a couple of times.
Having a Level 3 dispenser to fall back to will be mighty helpful for everyone.
Teleporters are probably less important before-round, but if you have nothing better to do, why not? 6.
(Heavy)
Ready a deployed Sandvich
As the countdown gets closer, a Heavy can alt-fire a Sandvich (or Banana etc) to throw down a temporary health pack near the spawn exit, then instantly fill the recharge meter by touching a resupply cabinet.
The deployed 'health pack' could provide a welcome source of health for someone retreating back in, including yourself or your medic.
7.
Have Fun!
Participate in (or start) a conga (maybe convince players (on both teams) to go for the Conga Line Taunt achievement ).
Play Rock Paper Scissors or give out high-fives.
Show off your taunts.
Leave animated gifs and memes on the walls.
Adjust your cosmetics.
Taunt at the other team.
TF2 is one of the only games
I know where it's both possible and encouraged to just...chill out and enjoy a moment
gaming.stackexchange.com/users/28182/Robotnik
Medics can build their ubercharge and that's about it.
You can only wait for the other team to setup defences for you to attack.
gaming.stackexchange.com/users/207152/georgeravenholm
Setup lasts a little over one minute in the asymmetric game modes. The defending team moves into positions, but when playing on the offensive side with casual players I'm not aware of any constructive action aside from building  ÜberCharge  with the medic.   The attacking team is locked inside their base until the round starts and the engineer can't build buildings.
What to do during setup as the offensive team?
gaming.stackexchange.com
<team-fortress-2>
gaming.stackexchange.com/questions/328316
gaming.stackexchange.com/users/204276/user176801
The setup time is designed for the defending team. There isn't really much for the offensive team to do other than build Uber and do the conga. On some maps, engineers on the offensive team can also begin building up their buildings. Taunting is also an option, among a quick trade, or even use the time to check on something in real life. There are a number of things you can do on the offensive team. You can of course build Uber and sometimes engineers can start building. You can have a look at how the enemy is setting up and there are also a number things you can do with the particular classes in the game.
Users suggest strategies to prepare while being the offensive team.