OK so I know this obvious but read ingredients on packets before you buy!! Having been vegan for 5 yrs and preivous to that vegetarian for 3 I have always been very careful with what I buy (as I was young when I became vegetarian what my mum bought!) however the other night i had soemone else cook pasta for me, this container did not advertise it had meat in it, infact it was labeled as spinach and something else, however as it was cooking I read the ingredients and in the middle, was BACON. It is so important to realise what you are about to cook or eat, even if someone else is cooking for you, however I believe that companies should make something like this noted on the front of the packet? rather than just in tiny print on the back.
I still forget to read labels on occasion & it bites me sometimes. It is really surprising the things you find gelatin in -- Jr. Mints, some brands of nail polish remover & pasta. Yep, I bought a bag of pasta that had gelatin in it. Go figure. ::)
My parents have a lot trouble buying whole-wheat bread when I'm in town, because 98% of the breads around here have whey in them, and that's one thing that they still forget to check for. That always makes for one of those awkward "Thank you for going out of your way, but--" moments... Poor parents. I think my veganism caused the majority of my dad's gray hairs. :P