You certainly could play in on mobiles, tablets and laptops, but I think you'd probably need more than even most people these days to get a suitable surface. But with enough devices, it wouldn't make a bad city-scape, it you stacked them - or used a non-flat device for the buildings, I suppose. Actually, tools and whatnot (screwdrivers, hand drills etc) might make for good crashed starship wrecks, it you pretend you're playing on a junk world (it's a bit more Star Wars, or... 40K, I guess, but for the sake of arguement).
You can go a long with with fairly-flat pebbles, actually. I got a load of 'em initially to play starships yonks and yonks ago (before they started saying "oooh, you can't take stones off the beach!") I dig 'em out again for this exact purpose, when I'm playing BT or MG Sci-Fi, they might grand little rock piles. (I now use asuqirum gravel for asteroids, but they also make a nice thing to sprinkle on the ground table occasionally.)
You could even do a good-old fashioned book-fort, though, like I made for me toy cars when I were a lad.
(Kids just don't do that these days...)
Anything really, so long as you get a decent density of terrain features. You imagination is your limit.