There's no reason, in theory, one couldn't integrate some retail, particularly food offerings, into some parks. (make sure you deliver the intended/needed parks program first, but its a solid add-on).
The only problem is that Parks has notoriously been terrible w/food vendors. The limited stuff they've done, in the Eastern Beaches in particular (I think its fair to say scandalous); but also in the Western Beaches and High Park, have generally under-whelmed.
That's fixable, we just need to poach people from City's who manage this well to set up a proper program here; same issue w/retail in the subway system.