How about a CG balance and incident meter. Not as critical on a high wing trainer, but another item to consider is a plane stand. If you fly from a busy asphalt field, you migh want to pick up a kneeling pad. Not so much for comfort but to keep your knee clean from all the fuel buildup in the pits. You will want to pick up a sets of standard and metric allen wrenches and nut drivers and a good sized wrench for your prop nut. Get some locktite! It's just amazing how quick all those fasteners start to work loose. I've lost a new prop and spinner in flight, and a screw off the back cover of my OS, as well as found loose engine mount bolts. 5 minute epoxy can be handy too.

Scott