We traveled across country in December, and I breastfed my then-2mo son on the plane on each leg. During takeoff and landing, I made sure he was sucking on something (either nursing or pacifier), and then he usually fed a little bit in the middle. It was simple, though the position was a little tiring since I didn't have my nursing pillow with me on the trip. I used a cloth diaper or receiving blanket for a small or large shield, depending on where my nursing breast was located in relation to other people in that row (ie, if I was nursing next to the window, I could use a small diaper for basic cover; if I was nursing next to someone else (not my husband) or next to the isle, I used the larger receiving blanket).
I also fed him at least once on each layover that was longer than a few minutes. I had manual pumps with me but found I didn't need them. The bathrooms were always in demand on our flight (at least, when I looked) and I felt bad even taking long enough to change him (though of course I did), so I wouldn't have wanted to spend the 15-20 minutes required to pump. But that may be just me. ymmv