1. Wizard porn
2. Mad Jack Vozza's Finest Firewhiskey
3. As many books as he can smuggle out of the library without actually having to turn Madam Pince into a radish
4. His wand, because magic that doesn't require putting his already terminally imperiled soul in further peril hath its charms
5. Assuming he could get one trained not to cringe or turn up at inconvenient moments, a house-elf, because he is one lazy bastard and if it cleans up after him then hey, one less thing he has to do around the flat