I'm looking at 3 day packs. Should I get one in multicam to match my OCPs, or tan to be a more discreet when traveling?

Go with black, camo pattern sure to change next year !

Your pack is not going to be the object that gives you away to being military (although it is a factor). Your haircut, mannerisms and walk will do that already.

Doesn't matter. As I travel around, there are so many people out there with them. Even in European airports I see lots of them. In the States, it's a forest.