Standard comms (VHF RTF, ADS, VOR, ILS) and a mode S would be S/S.
Depending on what you mean with BRNAV capability (GPS, INS, something else) you might need to add C, G, R, W, X, Y.
Most likely you'll be looking at SG/S. If you have anything fancier than that, you're probably in the wrong forum.
This is one of the hits that Google came up with:
Atlas Aviation - ICAO Flight Plan instructions directions information
In another thread a week or so ago we discussed the merits of the equipment field, and it was confirmed that ATC doesn't look at the field to decide what sort of routing they'll give you. Even if you only file S/S they'll happily clear you direct to an intersection hundreds of miles away. On the other hand, I have heard stories that the Eurocontrol computer will throw a flight plan out if your equipment doesn't meet the minimum route requirement, particularly mode-S.