Whats my next step??

My GF bought me a gift card to Drfosters and I have no idea what I should use it for. I'm wondering what type of equipment I should buy for my 40B. I already have a good light, filter, decent protein skimmer, auto top off, enough powerheads and not interested in a wave maker. What can I buy for around 50-100 maybe up to 150 to take my tank to the next level.

Thanks!