I've carried a variety of different backpacks and bags while wearing kiddo. For the first few months with an ergo, I slung a messenger bag (with clips for the straps, so I could remove it easily if necessary) across the opposite shoulder. I found that this put too much pressure on my neck/nerves and led to worse problems. I was able to wear a small backpack with the ring sling and sometimes did that.
I also did the messenger bag thing with the ergo. And I have the Ergo backpack. I wore it on my back with kiddo in the front carry for a long time, but eventually started using it clipped to the Ergo for an all back carry. Unfortunately, I stuffed the pack too full one day a bit over a year ago. I ended up doing something weird to my shoulders and collarbone and had to wait til I was home (another week) to see my doc and get adjusted. And then it was six weeks of no babywearing.

I now just carry a bag in my hands. Pain in the tush, but I'm not willing to go through that collarbone/neck/back pain again. I imagine it would be just fine if you're not stuffing it full of 30lbs of food, water, toys, and diapers, then strapping it on behind a 20lb toddler.

When I go to the zoo now, I take an umbrella stroller. Kiddo goes on my back or front, stroller gets the cooler bag and backpack/diaper bag, and camera bag. If kiddo wants to walk or ride, we can swing that, too.
We got the Deuter so that hikes could involve a bit more gear. It has pockets, a small built-in pack, and the hydration bladder pocket. Plus clips, loops, and straps for stowing/tying on more stuff. We won't be doing any overnight trips, but this could certainly do it if you packed ultralight and had a partner to carry more food/water and some gear.
With a small baby (3-4mo), I'm not sure how I'd swing a multiday hike. They really are too small for frame packs. You might be able to handle it with a wrap or front-carry in the Ergo with a separate daypack on back. Actually, that's exactly what I'd do--front carry Ergo with babe. Day pack with dehydrated food, ultralight camp stove, diapers, wipes, and maybe a small bladder pack (water is heavy). I'd carry the camera, too. Your partner will probably have to carry the bulk of the clothing, bags, pads, and tent/poles.
Don't forget trekking poles. and extra straps for lashing them on your pack or your partner's pack.