On Sunday, at least three families will be hosting stoop sales by the park. 44th Street between 5th and 6th will have lots of baby items (mainly girl, but some boy), knick-knacks, women's and men's clothing, and some household items.
Each is starting at about 10 AM, but the ending times vary. Come early to check out the wares.
Once you've perused the stoop sale items, continue up past 6th Avenue for some gorditas, pozole, and jamaica. Personally, I think it's the best food within a quick jaunt of the park.