In baby jail...ahem...I mean the playpen, only give the wee one either a couple of related toys (a few cars, a small pile of building blocks), or one larger toy (shape sorter, musical toy) at a time.
That's the basics of it. Engage his interest in the toy(s), showing off to him how he could play with it/them - though he'll be more creative in how he plays with it than you could ever be - and leave him with just that group/item for a couple of days, until his interest seems to wane, then replace it/them with another group/item.
Rotating the toys, as such, keeps the wee one from getting bored, as the toys seem fresh and new each time they are re-introduced. It also prevents baby from being overwhelmed by too much choice. Being faced with a huge pile of toys is as irritating to their senses as it is to ours to see such a huge pile - we see clutter and disarray and they also see chaos and no one learns contentment and focus in bedlam, unless they zone out - not something you want to encourage in baby or yourself.
;) One item/group at a time also cuts down on the clear-up ;)