210 MiB for a mini-CD, 155 MB for a low-density mini-CD, 30-100MB for business card CD (b-card) and there were actually some games released in this format.

I don't know about actually getting such niche formats though, so I could also see a normal CD being used for multiple games (even more with shared assets/libraries). Or perhaps placing high enough in a contest like this, they author it for you onto the disc (with disc+mini-case art) for you.