mazes are always an easy option, but my favorites were the ones where you could cutout game pieces from the box and use them on the board on the back

They'd be called Reimoos and they're little flakes shaped like cows with ribbons and lots of Touhou puzzles on the back. It would sell MILLIONs.
Wait, online games? What kind of cereal are you selling???

>>3552
>online games
There were some old cereals I remember that had either a cheap CD game in the box or had a code for a flash game on their website.

honey and oats and protein cereal for POWERLIFTERS with a table on the back for you to track your macros wherever you go and a shab with a little bit of nonthreatening muscle telling you that you're not good enough but you're getting there (she hopes)
included is a toy mini-scoop for you to collect, each of which has a random discount code for one the company's supplements

>>3553
Ohh, yeah now I remember. Some of them had codes you could enter and stuff. Pretty cool now that I think about it more