If you are running V-brakes then you will need to make sure your second set of wheels have the same rim width as your existing set. Otherwise the brakes may not line up properly.
Your complete shopping list:
- Spoke Protector (highly optional!)
- Rim tape x 2
- Tubes x 2
- Tyres x 2
When swapping the wheels over the gears should not need re-adjusting each time. You can also go for a different range, e.g. smaller closer ratio more suited to the commute. Your existing wide-ratio chain length should work fine. Depending on the level of wear of the chain you may want to get one of those too. You can check how far the chain has 'stretched' by putting it on the outer chainring and then pulling it at the point nearest the front. If this pulls forward 5mm or more then it is worn. This is a rule of thumb, you can get the posh tool for measuring chain wear or measure it with a ruler.
The other main benefit of two wheel sets is that you can service one set properly without being bereft of your bike. Not many people do it for mountain bikes, road bike owners tend to do this more in practice. The crucial thing to get right is the rim width, if your bike is a recent model then you can sometimes get replacement wheels from that bike manufacturer rather than have to get something specifically built up. Obviously if you are running disks then any wheels will do.