Xbox 360 Repair Kits
There are quite a few different kits available. However, the core contents are all the same. At the very least they will come with 16 washers and 8 screws. Some of the kits use more washers and include metal "lock" washers so you end up getting 24 total washers. Others just use heat resistant nylon washers exclusively, so there will only be 16.

Thermal Paste
Another basic item is the thermal paste. There are blister packs and tubes but all in all it is just thermal paste. The thermal paste is the most expensive component of the repair kits. This is why it is typically cheaper to buy a kit than it is to go out and buy all the components yourself. By the time you drive around and find everything you need, you not only have the cost for gas but the cost for your own time and not to mention the thermal paste is probably going to cost you at least $5 dollars and may even run you $10 dollars.

Opening Tools
A lot of kits offer opening tools as part of a "deluxe" kit. If you do not have basic tools laying around I could see where this would be a convenience. But if you do have access to basic household tools this is one of those areas where you could save a little money.

Cleaning Solution
Another "deluxe" item you will find offered with Xbox 360 repair kits is cleaning solution. Rubbing alcohol will work fine. This is a very common household item and another area where you could save a little money. Again, if this is not something you have laying around then by all means buy the deluxe kit.

Guides
If a kit is worth anything it better have step by step instructions included. Most do have instructions. Some send paper instructions, a lot of them have down loadable pdf instructions. Very, very few have video instructions. You typically have to buy an online repair guide separately for video instructions and they run about $15 to $29. There are free videos available on Youtube. See our videos section.

Conclusion
If you got a little mechanical dexterity and want to save some money, you really can not go wrong buying an Xbox 360 repair kit and fixing it yourself. You not only save money but you save time as well. Not to mention you will get back to gaming sooner than waiting for Microsoft to fix your problem.