As I don't possess any can anyone let me know what range of sizes

I should buy to cover simple tasks such as changing light bulbs

on a Yeti?

I am assuming other parts require them other than the rear light unit.

one suppled in the tool kit in the boot for rear light bulb changes,

Most trim bits are held on with t20 and t25 torx.

The door card screws are very deeply set. As these fasteners are becoming universal, I invested in a full driver set (including some odd sizes like T27) - they are just long enough for the door card screws. They also fit the security-type screws should you encounter any.

http://www.amazon.co.uk/dp/B0001K9VAO

Mark