Given that many ingredients in salad will go bad after several days, how can one store leftover salad so it is not wasted? Many vegetables, such as beans, lose their freshness after opening the can/package. A head of lettuce, can of beans, or the prepackage stuff is too much. For example, I can only consume 1/3 a can of beans each time...and I might not want to eat salad everyday (even once a day ). Will it help if I put the remaining beans in a sealed bottle? What about the vegetables? will they last for 2 weeks? 
Olives are naturally bitter and often fermented in brine to give a salty flavour - so they should taste bitter and salty.   American black ("California") olives are not fermented, which is why they taste milder. If you've never had European (fermented) olives then you'll notice a bit of a kick. It may be that you've never had non-fermented olives and the flavour was just new to you. Olives are an acquired taste.  Also, given that olives are either preserved in brine or fermented they're not likely to go bad for many years. They should keep at least a year, unrefigerated.  Read more about the fermenting process here. 