Best people to talk to are camper van conversion specialists. Google will find plenty of ideas.
As had been said you basically have a few options
1) 12V chargers for laptops, phones etc
2) An inverter to give you 240V. These will give you up to about 2kW capacity but you van battery will only last about 1/2 hour at that rate (if you are luckly) so in reality you are limited to less than 100W and even then you probably need a separate battery to avoid not being able to start the van in the morning.
3) A generator. Smelly and noisey and a last resort imho.
4) hook up to the mains at campsites
5) A combination of the above
Like I said, google is your friend, there are plenty of DIY conversions blogs out there to give you some ideas.
Personally I would use 12V chargers for phone/laptop/camera and LED lights for the van then gas for cooking etc. Possibly with a plug in inverter for those times when a mate hasn't got a 12V charger for his camera or whatever. Then make sure the van battery (preferably dual) and charging system is up to it. I'd also fit a warning system to the battery to let you know when the it is going flat.