The offerings used would depend on the spirit and intention. For Sitri in the manner you choose to work with him, I’d personally use anything that makes me feel seductive and dominant. In general most really dig art. You could write him a sexy story or poem, if you can draw, paint etc I’m sure he’d dig an erotic image.
You could set it up with perfumes, soaps etc to absorb some of his energy, and then use them on yourself to boost the effect. Offer him the opportunity to experience the sex you do get via invocation before hand. Maybe carry his sigil in your wallet/purse. Or a small version of his sigil in your bra?
He also likes incense a lot, scented candles, chocolate, wine, fruit, things like that.