As crazy as most cereal boxes are when they introduce characters and mascots, sometimes the non-traditional juxtapositions make for the nuttiest futuristic things you never thought you'd see as part of your cereal box fort.
1) Spock Sugar Smacks
2) C-3POs
3) PEP - The Solar Cereal
4) Quisp
5) E.T.
and as an added bonus... which isn't really sci-fi, but I imagine could get you high!