If you're not as mechanically savy as Dave and don't want to buy another tripod you can always employ a milk crate:
http://www.adorama.com/ADMC.html

If set on its side you can weigh down the base and reduce the potential of it falling over. I can't imagine a laptop could survive too many tripod spills.

2 options I"ve found are folding tables (where table top folds in half and has a carrying handle) that have polycarbonate tops instead of the usual particle board. Relatively light (under 10 pounds) and you can put all sorts of stuff on them.
You can find them at several outdoor stores . Target here in the US has them on sale. I just bought one for a shoot last weekend and it worked out great.

I forgot the second one...those camping tables that roll up and pack into a long narrow carry bag similar to those folding chairs. Not as stable, but much easier to haul around. I have one sitting next to my outdoor grill.

Here is an example from Cabelas outdoor store...
http://www.cabelas.com/cabelas/en/te...148&hasJS=true

Had a similar need and came up with this simple solution that works great
http://dvinfo.net/conf/showthread.php?t=102306