What equipment codes should I select? For example, is a G1000 a /P or a /S?

You can select multiple options for Radio Communication, Navigation and Approach aids, on the Aircraft page. In the Radio Communication section, choose:

S if your aircraft has a VHF comm radio AND a VOR AND an ILS receiver installed (all operational.)

G if your aircraft has a GPS receiver that is installed and operational.

If your aircraft has a G1000, you could select both S and G. Same goes for a GTN750, KSN770, GNS430, etc…; each would allow you to select S and G. However a handheld or portable GPS does not allow you to select “G.”