For hummingbirds, I recommend using a zoom lens in the 400–600mm range. You’ll be photographing from fairly close—often within 10 feet of the feeders—so you don’t need extreme reach, but you do want something that gives you enough working distance to keep a good composition and avoid disturbing the birds.
Personally, I often use the Tamron 50–400mm. It’s lightweight, easy to handle, and gives me great flexibility throughout the day when I want to switch between hummingbirds and other wildlife that might show up. That said, there are a lot of good options out there. The 100–500mm, 100–400mm, and 150–500mm are also popular choices among participants.
If you’re bringing a second camera body, I’d suggest pairing it with a mid-range zoom—something like a 70–200mm or 70–300mm. It’s great for spontaneous shots of other birds, wildlife, or even scenic moments that unfold while you're focused on the feeders.
Lastly, if you’re interested in doing any night photography or want to capture wider landscape scenes, a wide-angle lens can be a nice addition, especially during the fall when we sometimes get monsoon activity.