HTe list can be almost endless, depending on what type of building you do. For general purposes (no scratchbuilding) here's what i personally use:
Lots of good lighting
#11 Exacto knife with plenty of extra blades
Micro angled flush cutters, also known as "sprue clippers"
Assorted brushes, ranging from 0 to 000
Lots of paint
CA glue
CA disolver (of course, for my many mistakes)
sandpaper (various grits)
putty
sculpting tool / knife
paper napkins (cleaning brushes / spills)
ashtray w/ lots of cigs
Dr Pepper (the 100,000 gallon economy size)
Not exactly a complete list, but a good start.
demono69