Ring(s)! This includes your engagement ring (so all of you can participate) and if you have them picked out, your and your FI's wedding bands.
Here is my engagement ring, its a black diamond solitaire:

My full wedding set, FI had it custom made. The black diamond solitaire engagement, and then two bands for the wedding bands, above and below, each with rubies:

FI's wedding band. This was his father's wedding band. His father passed away 3 years ago and the band was passed on to him: