Chris. Most of the obvious stuff has been mentioned but here goes my list: cell phone, because some things just can't be repaired with a tool kit i.e. alternator rotor, unless you've got a lot of time and access to a parts store. The Harley/HOG atlas that gets mailed to you after the purchase of every new bike-it not only has maps of each state but it shows where every HD dealer is. Two spark plugs and a plug wrench-I found a cheap one at J&P for about $7 which will work in a pinch. A full set of English allen wrenchs, a pliers, an adjustable wrench, a knife, some tape, and any sockets/socket wrench that you can fit, normally 3/8" drive with the commonly used sizes: 1/4, 5/16, 3/8, 7/16, 1/2, 9/16, 5/8 and some combo wrenches, same sizes as above.
You should be able to fit all that stuff in a relatively small area. I know you have Sporty bags but when I went to Sturgis I brought all of the above plus a full socket set with every Metric and English size in both 6pt and 12pt (about 50 sockets), tire psi gauge, etc. and it took up very little space, although it was heavy. While I have never fouled plugs enough so the bike wouldn't start, I figured for Sturgis I better bring some plugs.
Some stuff, like the phone and knife I wear on me so no bag space gets taken up. The atlas and all the tools I listed should only take up about 10-15% of one bag. I always carry a rag and, for long trips, one bottle of water. Hope that helps. Luckily, the one time I was far from home and my Sporty died, I had what I needed to replace the battery. I made it home and a couple of days later found out it was the alternator that was really bad but I got to replace it in the comfort of my own garage.
My other suggestion is to do most of the maintenance and repair work yourself so you will get a feel for what you need in case of a breakdown. My list above comes from 10 years of working on my 96 Sporty. If you haven't already, buy the repair manual, it is worth its cost after just the first time you can avoid a trip to the dealership.
