I'd definitely take advance wars DS, it has many maps it would take anybody years to finish all of them, and then there's the map-maker. I'd probably take FIFA as well, as that never ceases to be fun online. Team Fortress 2 is also a cracking game which I could play indefinitely and I'd probably make it up to five with Star Ocean 3 (which is amazing) and probably Elite Beat agents as that is always good for a quick blast, although I'd probably tire of "jumping jack flash" after 10 years.