They would have to just hang out and not really be able to leave for 5-6 hours while our other friend is working, but could do their own thing. Basically they are just there for safety reasons if anything happens to our friend doing the work who we have a fair price established. First friend has a lot of sedentary hobbies so boredom isn't a risk but I want to treat them fairly.
Honestly, I feel like the correct answer depends as much on your ability to pay as anything. Among my friend group, I wouldn't expect any money to change hands, but if one or more of us was significantly wealthy, that expectation might be different.
I'm not rich but I got a union job a year ago but all of my friends are sort of oogles.