I'd say just about anything, at that age they are usually happy "helping" with stuff that needs more co-ordination or strength than they have. Stuff our Beavers have done:
- simple orienteering (N, S, E, W through a course of cones with gold chocolate coins to find at the end)
- building shelters and dens either with natural materials for their cuddly toys / mascot or with old tarps, sheets or anything you can get for them to sit under
- very basic first aid
- plaster casts of footprints
- firelighting (well, they do lots of collecting sticks and adults get to do the firelighting, then they sit round drinking hot chocolate)
- going for walks in the rain / dark / snow / sun