It completely depends on the bird. I wouldn't dream of not having a bell for Jade, but Clyde doesn't care about bells. For him, an essential is a rope and bead toy. He must have a happy hut, but Jade likes her snuggly ring. She has a boing but he hates anything that moves with him so he only has stationary perches. Neither one cares for foot toys.
We don't want your birdy to freak at all the new stuff

, but I don't know if you can streamline to three things until you know what he likes. So I'd say get several kinds of perches, maybe rope and a natural perch, and at least couple of different kinds of toys, completely different, say one with a bell and one that's just something to bang around and chew on, and try a Cozy Corner to see if he likes that. If he does, he'll probably like a Happy Hut. Don't bother with a mirror just yet -- some Quakers like them too much, and some don't like them at all. Neither of mine likes mirrors. My little Benjy would be a very unhappy budgie if he didn't have a mirror, though. He likes to argue with the bird in the mirror and Bonnie likes to admire herself but they're not obsessed with it. Clyde liked his (now Benjy's) for about two days and then ignored it, which is how the budgies ended up with it. Likewise, the budgies have a swing apiece and love their swings, but Clyde hates swings and Jade already has three, so she doesn't need another one.

You really just have to try various things.