KCDW, I have simillar problems with C172.
As the aircraft is run by the club, and slot times are a premium, (and I havn't worked out how to empty the fuel), I have to assume that the tanks are full prior to departure.
If I am taking myself (16st), fat knacker brother (18.5st), and flight bag (10lb), and assume full tanks, then I have 6lb to spare on take off !
Incidentally, the aircraft handles well, but I notice that I need lower nose attitude on initial climb out.