Something like one of these http://www.amazon.com/sabrent-Converter-Supply-Activity-USB-DSC5/dp/B000HJ99DI

On my phone so I can't copypasta the actual links to my bag, but it's detailed in this post with pictures included.

http://www.reddit.com/r/computertechs/comments/12acox/starting_my_own_pc_repair_business/c6ti4gx

EDIT: Contents of mentioned post

Get yourself a few USB drives and turn them into bootable drives. I have one that will install any version of vista, one for 7, and one that has a ton of utilities on it (Hirens, UBCD, etc) and the Windows XP installer. I also carry a laptop with me that dual boots Win 7 and Linux. Linux is really helpful when HDDs go to shit and Windows won't mount them anymore. Grab something like this Husky Case as well, and fill it with the aforementioned supplies (cables, canned air, laptop, forms, etc). I can post a picture of mine if there's any interest.

EDIT: Pics as requested

Case Exterior

Case Interior

Exterior Parts List Interior Parts List GRID-IT

1. Generic Laptop
2. 7 Pocket Portfolio
3. Husky Tool Case
4. Pliers
5. Normally Closed Tweezers
6. Dikes
7. iFixit 54 bit driver set
8. Zip Ties
9. Pens
10. Sharpie
11. USB Wireless mouse
12. Multitool
13. USB Mouse and Keyboard
14. VGA Cable
15. PSU Power cable
16. Laptop Power cord
17. Canned Air
18. 8GB Flash drive
19. Microfiber cloth
20. Adhesive Zip Tie Mounts
21. Computer screw kit
22. Adonit Jot Stylus for phone
23. 4sevens Preon P2 Titanium
24. Business Cards
25. Lock
26. Blank DVDs in Sleeves
27. Extra Batteries for Flashlight
28. Spare WiFi card
29. RJ-11 Phone cord
30. Laptop Battery
31. AC->HDD power adapter
32. IDE/SATA -> USB adapter
33. Laptop Surge protector
34. RJ45 Cables
35. USB A->B cable
36. HDMI Cable
37. Mini USB Cable
38. SATA Cables
39. GRID-IT
40. Generic Card Reader
41. HDMI to DVI
42. Patriot 16GB geek drive (all bootable utilities)
43. Patriot 16GB Windows 7 Install Drive
44. Patriot 16GB Windows Vista Install Drive
45. Square Credit Card Reader
46. Headphones