In addition to h22's crackers, (
) avoid camping at established, heavily used sites if at all possible. We use floorless shelters almost exclusively and mice have only ever been a problem once. A regularly used horse camp.
Or, bring a few mousetraps and a little peanut butter, the traps weigh nothing. We had a problem once at one of our camps that wasn't used at all, just a good west-facing aspect with tall grass and lots of mouse food. A mouse chewed through my buddy's longbow string, put him out of business. Next season we brought three traps each.
As soon as we settled into our bags the first night, they started going off. Second night was quiet.