Rev's are pretty darn durable. The only thing I would recommend is maybe a couple extra spars just in case, a replacement bridle because they will wear over time, some of the washers (sail washer, bungee washer) and some replacement end cap kits with bungee's. All can be purchased for under 50 bucks and should last you for months if not years before you need them (except the spars if you are extremely abusive).
One leading edge center spar and one other spar. In the thousands of hours we have flown, we have broken only two spars, one leading edge center when we hit each other head on,,,,,,,,hard, and one vertical spar just exploded into four pieces. I think it may have been defective as it was a three wrap and the wind was not high.
One pair of end caps. They come in pairs and are all the same cups. Any one of the pairs sets will give you two extra bungies as well. We have had only one fail.
A few of the rubber washers. Use rubber faucet washers available at any hardware store or get nylon washers to use as replacements. Nylon washers will far outlast the rubber faucet washers. These are the parts that seem to give the most trouble. For easy and quick repair on the field I carry zip ties.
I carry super glue to re-glue the leading edge ferrules when they work themselves free due to flexing of the leading edge over time. I remove the leading edge center spar every so often to check that the ferrules are still glued in tight.
Extra bridle. I tie our own bridles. Bridles are made of three separate pieces. Left and right verticals are interchangeable. I replace sections as needed. They really do last a long time. but should be looked over for ware. A bridle failure in the air is not pretty.
As stated before, these kites are very durable and take more crashing than you might think. Just learn that the bottom "brake" lines are your best friend.