First Time on a Sag Production. Tips, Etiquette?

I’ll be doing background work on a SAG set for the first time. I have experience doing speaking roles on non-union indie features and shorts but I’ve hardly done any background work and never on a SAG production so i just wanted to ask about general etiquette and flow of the day. How early should i arrive, what am i allowed to bring to keep myself entertained, any other tips, etc.? Also, this is a voucher spot so I wanted to know how to collect it at the end of the day. Don’t want to bother the wrong person…