If bio's are a field requirement, it will always be posted on the game thread. Also bio only field will typically have field BB's or possibly a field Bastard in respects to Flag Raiders at all games.
Yes, there will still be some places that have no preference so having some of your favorite styrene supply on hand is a good idea.
One thing with bio's is that you'll need to be mindful of how you store them. Keep them dry and out of the sun. Unload left over mags and try not to reuse them if you just played in a wet game. Or at the least, don't mix them with your dry stock.