I recently posted about bringing your own container for leftovers when eating out (which I still believe is very worthwhile) but I have also been dwelling on the what container to buy, use or reuse. Some plastics can transmit chemicals into your food/drinks.
This Green Guide breaks down (no pun intended!) the seven types of plastics, you know that number on the bottom of the container. Generally it is #1, 2, 4, 5 that are safer plastics but note that #1, 4 and 5 are often hard to find a place to recycle them. #7 is miscellanious but those that are made with PLA are very safe and renewable – made from corn, potatoes, sugar cane, etc. and can be composted breaking down in less than 2 weeks. Plastics #3, 6, 7 (all others besides the PLA items) should be avoided.