I rarely use any on the kit these days, but sometimes play only aux. percussion at jam sessions. Then it's an LP Mambo bell I found used, a serious low sound. Should put it on my set for some Gadd action
For some time I used a combination of tambourine, red jam block and a smaller cowbell as add-ons with improv music. This combination seemed to complement the 4-piece drum set sounds well and also added an element of slapstick humor.