If you do buy formula, consider the powdered type. It lasts longer and you can mix it up as you need it. I would put the powder in the bottle and carry water separately and then blend them. My oldest had a breast milk allergy so I couldn't nurse him. I did nurse the others, but ALWAYS covered up for my own sake, not because I was ashamed of nursing but because I considered it a private activity between myself and my child.
By the way, my mother told me that the most popular formula when I was born (1959) was Karo syrup and evaporated milk so you are lucky you nursed; you may have avoided the awful sweet tooth that I and many others raised on that drink have!
As for other stuff, Costco sells cheap diapers and wipes. The sippy cups are great. I would not buy clothing as those are probably available at a thrift shop or second hand. Sorry but even when I earned 6 figures, I bought my kids' and most of my own, clothing at consignment/thrift.
Another nice thing for toddlers and pre-schoolers would be picture books as that is an area that is often neglected when people are struggling to feed their kids.
I ran a food drive a few weeks ago with my Boy Scout sons. Even in my so-called upper middle class suburb, there is still an amazing need. I also had to work through the Church, even though I am not the only Jewish person in town. They just seem to be set up better for that kind of thing. My temple collects food but then gives it to the church to distribute.