Greetings from a fellow judoka.
There's some good advice on this thread, so I'll just add some more suggestions:
towel pullups - if you want to be more judo specific, try using your gi instead of the towels. Works wonders for the grip. Farmers walks are also excellent.
High-rep dumbbell/kettlebell swings, snatches and clean & presses.
Burpees are essential, they have a tremendous carryover to judo. Do them in different formats - ladders, 30 sec on/off etc.
I don't know how your classes are organized, but we occasionally do 10-20 burpees immediately before randori as a pre-exhaust method.
That was just some random and homefully useful stuff from me.