Single Engine or twin engine. DC devices can run off of the battery. AC devices can run off of an inverter, within reason. A/C, Heat, Electric Stoves, or anything with a high amp draw (combined with the amp loss from inversion) will mean short runs times.
If you plan on a lot of amp usage away from shore power a decent sized dedicated house battery bank is a good idea. You can install an Automatic Charging Relay to allow the alternator to charge multiple battery banks. How much amps you intend to use and how long you stay out will dictate if a generator is a good fit.
We wouldn't go out for more than a single overnight without a generator.