One trick I learned from a mechanic. On the last part of the tire install, maybe 7 inches left to go, try soapy water. This gives the tire the slick surface to make that last part easier. Since its not petroleum based, it won't hurt anything.

In my bag, I carry an old small bar of soap in a plastic bag. Even with spit, I can mount the tire while on the road. I take the bar of soap, still dry, and rub it on the outside of the rim and some on the bead. Then add a little water from my water bottle, or even spit. That's enough to make things slick.