I flew alone with my 7 months on 2 flights:12hrs and 7hrs
Here's how I managed:
For one flight, I only ate when my son (7 months) was asleep in my arms. I called the flight attendant and she brought over my meal. Manage to eat/drink with one hand. I did not drink from cups and only drank bottled water. Easier that way. I also booked the flights around his bedtime.

For the other flight, I was lucky to have a free seat next to me, so I used the other folding tray.