If your selling food regardless of cost you will have to comply with health and safety regs. Will still have to have a registered business and still do tax returns.
Most small business do not pay tax due to all the lovely deductions.
This is a simplified version of what that UK says, since Kingrow is talking UK.
You make the occasional pizza and feed friends then fine, no big deal. You create any sort of organisation that supplies pizzas on a regular basis, even as a charity so nothing changes hands, you still have to comply with health and safety, food safety, environmental protection and all that jazz. So if Kingrow is even handing out free pizza he will still be illegal unless he complies with the aforementioned regs. If anyone doesn't believe me, I can find plenty links to prosecutions and "cease and desist" orders against people doing all sorts of home produce for charity, never mind at "breaking even".
Now that's just pizza, and not what will be a controlled substance. Anyone who thinks legalisation means a free for all seriously needs their heads examined. There will be restrictions on sales, anyone supplying will need to be licenced, anyone doing any form of retail or distribution to the public will have to be licenced. Even if he was handing out excess for free, it will still be under distribution so he would have to comply with each and every regulation regarding distribution and retail. Any deviation from whatever laws are in place and he can be nailed for it. Undercut "legal" outlets by selling "excess", whatever laws are in place regarding distribution, supply and retail would have to be fully complies with or, no matter what, even handing out excess for free would be illegal.
That's why I don't think I could hammer the point about how it depends on what theoretical laws are in place, for that is a hell of a set of variables which cannot be accounted for, in with the use of a pile driver, as it's what any theoretical laws I'll say regarding supply, distribution and sales which decides what side of the legal fence he's going to be on.