Well, for starters, you need to tailor it to your specific weapons but:
makes a complete range cleaning/oiling and greasing kit you might want to look into.
Gun Cloth ( or other protective surface that can be unfolded and laid down to work on the piece in question )
Pen & Paper.
Lots of patches.
Brushes for your different calibers.
Lens Cloth for optics.
Lots of Q-tips.
Plenty of spare earplugs - even if you wear the muff style, you never know what cannon the guy in the slot next to you is going to bring in.
Extra pair of glasses - Just in case
I like to keep about 4 pairs of surgical gloves in mine, just in case I need the extra "traction" with small parts.
A couple of good quality small screw drivers ( phillips and standard ) probably a large and small blade of each.
A small torx head screwdriver kit - Could be combined as one kit with the screwdrivers above.
A small plastic tipped hammer.
A few brass punches ( tiny, small and medium ).
A small box/bag of replacement springs/detents/etc. Basically an "Oh Crap" bag of anything that you have ever dropped, misplaced and spent 20 minutes looking for when doing work at home.
A 1911 Barrel Bushing Tool - Even though you should be able to field strip one without it, it's a great tool to have, just in case.
That's just off the top of my head as to what I have in mine. YMMV.