I'm about to go on a 2 week tour - this is my list which looks like it's heavy and bulky, it isn't!
Tools:
Plastic gloves
2 off Tubes (for tyre size)
Puncture repair kit
Tyre levers
3 off CO2 cartridges & connector
Pump (mini track pump housed in frame seat tube)
Folding tyre 700 x 25 [The spare folding tyre is as emergency cover for the whole group of 11 and we'll take it in turns to carry it]
Chain splitter (in light alloy multi-tool)
Multi-tool
3 off Magic chain links 8speed
Oil (3-in-1 spray)
Rag
Cable ties, nuts & bolts, tape
Kevlar replacement spoke & key
Cassette removal tool (Unior)
2 off Toeclip straps for attaching anything
Waterproofs/Clothes:
Jacket (lightweight, windproof)
Jacket (clear PVC "racing cape")
Helmet cover
Rainlegs
Arm & leg warmers
Spare gloves
Misc:
Lock & cable loop for helmet locking
Strap for holding bike on train
Spork
Swiss Army knife
Mini First Aid kit
Sterilising tablets
Medical kit/pills (personal)
Suncream
Rob