A couple of notes. Lights should all be 12 volts and should run off the battery. If they don't work I would start there. Could be a battery disconnect switch accidentally activated, blown inline fuse at battery (if there is one). The battery should be fed to the fuse panel (not circuit breaker panel) and from there it will be routed to all 12 volt items.
The 120 volt section is separate from the 12 volts. Either shore power or generator power will come in and be connected to a transfer switch which will select one or the other. If the generator is on it will select that feed to pass through to your circuit breaker panel.
The circuit breakers will route the 120 volts to all outlets. The GFI outlet, which may be in your bathroom, only protects some of the power outlets if it trips. Those most commonly are in the kitchen and bathroom, mostly outlets that are near water. If the GFI trips you should still have 120 volts to many other outlets.
So, where to begin? I would first try getting the 12 volt side of things operational and then work on the 120 volts. Remember, the 12 volts are protected by fuses while the 120 volts are protected by circuit breakers. You can try resetting all circuit breakers.
Please let us know what troubleshooting steps you have gone through so we can offer additional tips. A multimeter is a must have tool for all RVers!!!!!
Last thought - your 12 volt side of things can be powered by the converter which is the gadget that converts 120 volts to 12 volts. If there is no 120 volts it will not work at providing the 12 volts but the battery will still do the 12 volts.
Retired electronic technician (45 years in the field)
2017 Greyhawk 29W
solar & many other mods
wife (maybe I should have given her top billing)