The essential multi-purpose screwdriver. All sort of set can be found in your local shop or on the internet. Try ebay or google for precision screwwdrivers.
You can see all the different bits you have. It is essential to have at a extended set because the objects you are going to dismantle will always have different screw types.
To dismantle things a bit bigger, you will need bigger tools. Here a set I have and which is extremely convenient as when packed does not take too much room.
The full set. It is extremely easy to change from one bit to the other.
Here a close up. See the numbering from 0 to 5. The bigger the number, the bigger the screws you can unscrew. Theses are not precision tools. You can dismantle anything with them.