I haven't set up my altar much at all yet, aside from a black bookshelf/table-like space with a candle. Most of my spirits and spelled items are in one of two wooden boxes. The first box I've been adding to for years and when you open it, it expands into several little shelves. I just keep rocks, herbs, little spells, bones, etc in there. Then I have a square cigar box that I really like. It's very cozy and smells wonderful inside. that's where all of my spirited items are, in pouches if they're rocks/easy to lose. It's filled with gemstones, some of them given to a specific spirit and some of them just general offerings. I also give twigs and leaves... things that they seem to be drawn to. Both boxes sit by the altar area. I'm pretty poor and have always lived in a similar way to the way I keep that box- everyone has their own things but shares, respects each other, etc. I treat them the way I treat my human family and friends. That's just my instinct. They seem to be content with their box for now
I think sometimes people get nervous about things like that because they assign living, earthbound human characteristics to their spirits (thinking an offering might not be good enough, or that your spirits are mad because you haven't had time for them, etc). But at least as far as mine go, they appreciate any effort I make and honestly aren't picky at all to my knowledge. This could probably differ from spirit family to spirit family, I only know my own.
I do plan on making a general but more established altar for working with them and spells. I'm excited to set it up a bit more when I have time