There are several lightweight amps.
Genz Benz just came out with a couple of small combos. One of them is only 13 lbs (300 watt head and 8 inch speaker). They also have a 10" version that weighs 18 lbs.
www.GenzBenz.com
Also, Henriksen has a small combo amp that is supposedly very much like the old Polytone amps. I believe Bob G sells them.