I use a tool like this (Kool Stop Tire Bead Jack) to get the tires on the rims, for Gatorskins and some other brands.
http://www.amazon.com/dp/B001AYML7K/...l_443sewmx4l_e
It's not small, but it is lightweight.
Another good tool is the VAR tire lever, though I don't know if that's available any more in the US. It does the same thing as the Kool Stop but is smaller so it fits better in a bike bag.
I think some other companies also make a tire lever that is designed to help you get the tire onto the wheel. Regular tire levers (made to help you get the tire off the rim) can also be used, but there's a risk of puncturing the tube.
- Gray 2010 carbon WSD road bike, Rivet Independence saddle
- Red hardtail 26" aluminum mountain bike, Bontrager Evoke WSD saddle
- Royal blue 2018 aluminum gravel bike, Rivet Pearl saddle
Gone but not forgotten:
- Silver 2003 aluminum road bike
- Two awesome worn out Juliana saddles