One very cool trick, that i learnt from a truck driver on a remote road in Karnataka......
if you have a flat and while unscrewing the nuts from the wheel, the nut slips, pack some sand into the spanner (won't work if you have an open ended, or a regular ring spanner, but most repair kits come with the capped type ring spanner) , and then try and remove the nut....works like a charm............
