It is not officially recommended to reuse single use master chain links, but in reality everyone re-closes them all the time (even roadies, I read somewhere). The worst whatthat can happen is that the life span of the master link will decrease after reuse, but you were about to throw it anyway ending its lifespan. Carry a spare new one with you so that you can replace it in an (unlikely) event of breaking. Just don't sue the manufacturer in that case.
If stakes are high and you are in some serious competition, obviously you don't want a mechanical problem; otherwise, you should be prepared for on-trail repairs anyway.
The last thing: do not carry old master links over to a new chain. if you throw away a chain, its master links go away with it.