If you're looking for some entertainment and nostalgia at the same time, check out Kraino. Yes, this is the same game from your childhood, if you're old enough. This is one of the original "platformer" style games, and it's a blast.
A blast from the past, at least. While you only get six levels in the mobile version, they're all worth playing. The game is easy to pick up and play when you're bored, and it works without the internet. Get through some checkpoints, then battle the boss.