I bought a bunch of biscuit packets (ginger nut, digestives, bourbon biscuits) and couldn't resist opening a pack or two to try them. Now I'm afraid they'll go stale if I just leave them half opened. I have Tupperware but not super airtight or high quality. Nor do I have any dedicated biscuit tins. Should I keep them in the packet or transfer them somewhere? Can I use a glass pickle jar?  What is the best way to keep biscuits fresh? Any tips on making a DIY tin? 
A traditional method, used by my mother, which seems to be quite effective is to add a few sugar cubes in to a container with the biscuits. The sugar absorbs some of the moisture there by extending the life of your biscuits. This however is only effective if you are using an air tight container. 