If you are going into battle and at risk for not having sufficient mounts - have a couple people carry a stack of steedgrass and a whistle. It's lots lighter than extra mounts. Especially if you don't know if you are going to have access to a bank. Everyone gets excited about making mounts - the new weight issues changed that save some grass for carrying.

Wildtribe mages were THE best source of grass imho.

Everyone reread Kay's comment - farm gold not grass and buy what you need.