Only if its washed sand - unwashed builder's sand contains some elements that are not good for plants, so if you don't want to plant up for six months, it'll be okay, but not otherwise. Doesn't do much for clay soil anyway, sharp grit's much better.

I agree with Bamboo but if you've only a small amount of 'leftovers' I doubt it would be a problem if you spread it over a wide area. Could you keep it somewhere, it's useful for re-laying slabs.

peat even better or humas as in well roted manure, why not become a member and learn as you go alonge ,cost nothing and we are frendly.