I guess you pack your lunch.
Not likely there will be a pizza delivery and running to McDonald's for a burger and fries would be a pain.
I actually asked him about lunch on the job once. He said they had a canvas pouch hanging from the back of their belts and that they just carried their sack lunch in it. The light bulbs were in a bag also hanging off their backs so that they wouldn't bang into the tower and break. The harnesses they used allowed them to lock-in and sit stationary to work, rest, or eat.
The reason for the 8 hour time consumption, he said, was that they were also inspecting the tower joints and wiring on the way up. As a side note, the company he worked for also did the high voltage electrical tower inspections from helicopters. He said he tried his hand at that, but didn't care for it much.