for me on the move i love MAME32 and all those old coin op classic roms that are available.
http://mame32.classicgaming.gamespy.com/
you can get roms here.
http://www.rom-world.com/
I have about 800 plus original coin operated machines on my laptop and combined with a joypad its served me well on many a travel.
RTYPE still as difficult as I remember as a child!