Spend the money for the inverter on a 12v laptop charger. Its not efficient to convert 12v to 240v, then convert the 240v down to ~19v for a laptop.
Get 12v lights, not 240v.
Inverters are inefficient and don’t like it when the battery isn’t well charged. They also drain the battery whilst on standby.
In six years or so of campervan ownership, my inverter was used for:
1) Laptop
2) A jigsaw as I needed to use it in the middle of a field (it didn’t run properly as I don’t have a megabucks pure sine wave invertor)
3) Electric Toothbrush (killed two before I worked out it was failing to charge after being plugged into the inverter)
Other stuff that don’t like cheap invertors:
Fluorescent Lights
Battery Chargers
12v LED van kits can be quite cheap, I got a set similar to these and put them in a horsebox, they chuck out a decent amount of light…
http://www.ebay.co.uk/itm/Car-Light-Kit-Interior-12v-White-30-LED-for-LWB-Van-Sprinter-Ducato-Transit-VW-/161954134867?hash=item25b537fb53:g:dLEAAOSw3KFWgF0z