A lathe, altough handy, isnt at a high priority. stuff i can think of, that will almost certainly (some of which you have);

General Tools (screwdrivers, pliers. files etc)
Angle grinder (a must if welding)
MIG welder
Jigsaw
Hacksaw (with good blades, cutting through 6mm S-Steel with a blunt blade takes along time)
Good pistol drill (cheap ones tend to burn out quickly, we blew two up when making Merlin so just bought a cheap Bosch and had no probs.)
Hammers (of all sizes, bigger = better)
Basic electronic stuff (meters, irons etc)
Good set of spanners and allen keys
Good set of drill bits (cheap ones tend to blunt easily)
Set of taps
Big vice and work surface
Lots of gaffa (its even needed when building).
Lots of pencils (you will be amazed how many you loose!).
Bench Drill (saves trying to drill a straight hole by hand, you can cheap ones for about £35).

Theres alot ive forgotten.

In our experience it doesnt pay to buy cheap stuff, you will end up having to replace it at some point. You might save yourself £10, but the it could break the night before an event leaving you stumped! Some items that you wont use as much, you can get away with cheaper stuff.