Do I have enough clothes? Will the clothes be able to be worn with multiple outfits? Will they survive an Amazonian jungle while I fight off a swarm of prehistoric, tribal ants?
Grey cotton tees are definitely an asset if you are running off in warm weather and planning to around doing a lot of active sports — things that you're probably going to sweat up a storm in. They're also great to wear in a casual setting as well as for adventuring outdoors. I recommend getting a pack of grey or black V-neck cotton tees for this sole purpose.
These fairly cheap shirts are comfortable, match practically everything and are easy to wash. I brought a package of these shirts with me to Nicaragua as my only tops and it lasted the entire three months that I was there.
It might be tempting, but beware of buying the white shirts. Let's just put it this way: after some cavorting around in the ocean, the white shirts had magically turned into tan-colored tees. (By that token, you know what happens when a white shirt gets a stain. Ahem.) At least I didn't feel too bad about leaving those shirts behind.