I rack my brain every time on this subject.
I've done 4 IMs and never went to pick up my special needs bag, until lthis last one.
It was a really WET day and I had put plastic baggies and fresh socks in my T2 SN bag...but guess what ?
IT WAS GONE! I don't know if it was taken out, or fell out...but I was sort of bummed.
So I slogged away in my soggy shoes. I did eat the extra Powerbar though :-
)
My thoughts on T1 bag.
Anextra tube and CO2 is common, and a decent idea if you happen to flat in the first half.
Extra salt pills in case you drop or forgot them. Any special nutrition you might want
(also in case you drop it
).
Pain reliever if you happen to get a knee or muscle problem, but most of those sort of issues happen later than special needs pickup.
An old tire, in the rare case you slit your sidewall
(happened to me on a short prep ride
)
As for T2 bag.
Upset stomach pills, pain pills, extra salt pills.
Special incentive food and or drink.
extra layers if it gets colder
extra socks
(but the shoes are probably wet too, so may not be worth it
)
light if you plan on being in the dark.