There are a lot of things that are cheap and plentiful today that would be very valuable back then. Sugar would be very valuable, especially refined white sugar. Drinking glasses and other glassware would also be very valuable, as would silk, both plain and patterned, and almost any spice, pepper, nutmeg, cinnamon, etc. Dyes would be good too, but you'd need to show they work.

All these things were available, but even the rich would have trouble affording the high quality stuff we have today.

Strong spirits wouldn't go wrong, but you'd have a hard time convincing people of the quality if you only have a day.

Plastics and polyester stuff might go down really well, but you'd probably need more time to convince people how good it is.

Later on aluminium was very expensive, but during the renaissance, people probably won't know or care about it.

As for what to bring back, gold and silver is always a safe bet. If you had more time you could commission some artwork and bring back a painting or sculpture. If you're even more ambitious, bring back a dodo or two.