My adult cats don't "play" much anymore. But when they were younger, they loved cardboard boxes -- I cut holes in them, so they could play "peek-a-boo" or "gotcha" (alone or together). Sometimes, I stacked the boxes and taped them together, so the could climb through the holes (inside) without the boxes toppling over or the holes misaligning.
They played with almost anything that moved -- wads of paper, bottle caps. I found that store-bought toys were a waste of money, except for a couple balls. One had a bell in it. I took that away from them after finding the only times they played with it was 2 in the morning. The other ball was a sponge ball. One cat, in particular, would carry it around for hours and cry, like she had to dispose of a bomb. The ball got lost and I haven't been able to find more.
My cats, no matter what age, love cat trees. I bought some, but also made my own out of supplies from Home Depot.
Treats? I recommend "all natural". My cats love raw fish, raw chicken, cheese... I don't give them store-bought anymore. I've decided treats, like the ones I just mentioned are much healthier for them.
My cats love fresh catnip. I planted seeds in pots and they nibble on them whenever they desire. (Of course, they've chewed the plants down to half-inch sticks!... But, I planted more!
If you want to buy packaged (dry) catnip, my cats liked "Smarty Cat" and "Frontier" brands (and there are other good brands). However, I bought "Frontier" in bulk and they changed the grind. It's now like fine saw dust,,, or smaller than sand particles. My cats didn't like it, at all. That's when I started growing my own. "Smarty Cat" has been faithful.
I guess that's all I can think of for 5 o'clock in the morning [ET].