In reply to usmaniac:
So you have a rope, a krab and a sandbag but no harness?
To top rope you could body belay or take a turn around a tree or form a belay using the rope to 'sling' an anchor and the krab/Munter hitch to control the toprope or just keep walking back from the edge on flat ground as the second climbs. In the past I have once resorted to lying down in a hollow and rolling over and over to wind the rope around my body as the second climbed so the 100+ mph rotor I was exposed to at the edge of the mountain didn't whip the rope away and tangle/freeze it into the boulders behind.
To belay a leader improvise a harness with the rope, a sling from the leader's rack or a combination of both then control the lead rope with a Munter hitch on a locking krab. Without a locking krab a pair of back to back snapgates and a hex as a belay tube is another option.
There are loads of options in both cases.
Your mention of a sandbag suggests indoors in which case I'd hire or borrow the right kit before I got kicked out.
jk
Post edited at 11:54