get a pair of synthetic travel pants (lightweight) with zip off legs. The can double as camp pants/ foul weather pants, and if theyr'e still clean enough, dinner wear.
dump the tshirts, carry two or three jerseys and a long sleeve capaleine. The capaleine (or other synthetic) is good camp wear and okay for emergency bike wear.
Dump the sweater and get a wind-fleece jacket. With the layers you have you can ride in the snow. (Definate overkill)
Tent, sleeping pad and bag are fixed. (not much to reduce unless you buy new.)
unless you're unsupported for days or riding in the winter you should only need two panniers. Okay to use 4 small ones with room for food and water.
most people carry WAY too much. (I carry too little)
don't forget...
electrical tape. (wrap about 3 feet around a piece of gear (film cannister, mug etc)
duct tape (just get a flat roll from the hardware store, tiny but enough)
dental floss (crack open the box, just carry the roll. It's not much but i've tied tarps with it, done small repairs, tied cables in place, made tripwires in the jungle (oh, that's actually not when i was cycling, (or a civillian)
Meds, (the blister pack variety are best, two of most anything is still tiny)
TP. Like matches i carry two sources seperately. Camping stores sell tiny rolls.
Band aids, steri-strips, a few betadine swabs. In case of a bad rash out in the middle of nowhere wash with high pressure water then drop a few betadines in water for 5-10 minutes and irrigate again. Steri strips will keep a laceration in place (just clean it first) until you get stitched. (total size a book of matches)
a book of matches.
a presta to schraeder adapter (ask at the bike shoppe, if your pump fails you can use a gas station or a motorists auto pump.)
a tire boot (you can always use the duct tape but these are better)
kevlar spoke (tough to use but tiny and can get you out of a tough bind.
(By the way the whole list above fit in one squished sandwich bag on my last trip)
hope i didn't miss anything.
oh yeah, in the same bag, spare credit card, $100 cash and a photocopy of your drivers license. If you get ripped off your toiletries bag can save your butt.