An eternal problem I have is keeping my jeans tucked into my jeans properly. Even skinny jeans bunch and creep around.
Per a reader request, I have found some solutions. Here you go:

hold-downs1.jpg
http://www.suspenders.com/motorcycle-gear.htm

* Fold the fabric over and safety pin it.

* Elastic jodhpur straps from horse-riding stores:
http://www.legacytack.com/p/10477/
http://www.doversaddlery.com/product.asp?pn=X1-3711&cn=1903&bhcd2=1199481684

* Some people recommend pulling your socks over your jeans, but I find that creates uncomfortable bumps. I think it works better with thicker socks, though.

* I also heard it helps if you are wearing regular jeans to roll them up and put them in the boot. That keeps them from getting bunchy.