Questions are great.

Vampires can, in this lore, be of any age, but I'd rather keep it within the last two thousand years. Anything else feels a bit ridiculous to my mind.

Blood bags (of a sort) are definitely sold. I'll add this info to the OP because it's a great point.

[list][*] Organic produce: find a volunteer and go wild. Just don't kill them or seriously injure. Vampires can make this a very euphoric experience akin to (or even as part of) sexual intercourse, so there would indeed be a good few volunteers[/*]

[*] Take-out: go to your local blood stockists and pick up a bottle and swig at leisure. In my head, it's basically sold in bottles like wine. Since many of the blood-letting clinics are privately-owned, there are basically different brands.[/*]

[*] Dining out: in vamp-friendly bars, they pull pints of it, freshly let (typically better than bottled - preservatives make it crappy), sell a bottle of a recognised brand (see above), and there are often humans willing to have the experience of being nommed, either for kicks (high-quality establishments) or for money (low-quality). Chowing down in public is just rude, though, so bars tend to encourage their clientele to hire one of the rooms provided.[/*][/list]