RON stands for Re-open Nominations; it means you'd rather have a fresh set of candidates to choose from than have any of the remaining candidates.
You can still rank further candidates after RON:
- Five Guys
- Las Iguanas
- Pret a Manger
You're saying that you want to go to Five Guys or Nandos, but if not those two you'd rather go somewhere else entirely. But! If the group is going to insist on one of Las Iguanas or Pret, you'd prefer Las Iguanas.
Do I Have to Choose RON?
No! you can just order the ones you care about and leave the rest, you only need to use RON if you really think a different set of candidates would be better than the ones on offer.