Per diems cover what the tour does not feed you, plus the coffee, laundry and taxi that come with the day. Paid in cash at the start of a run, or weekly on longer ones.
What it is worth
In Europe, €20 to €40 a day is normal for club touring, higher on long runs and in expensive cities. Musicians and crew are usually paid the same rate. Some tours pay only on show days, others on travel days and days off too. Whichever it is belongs in writing before the run starts.
How it sits next to catering
A per diem is not a Buyout. The buyout replaces the venue's catering for one show and is paid by the promoter. The per diem comes from the artist's own budget and runs whether the venue cooks or not.
Tax and admin
Several countries treat reasonable per diems as untaxed expenses up to a published daily rate, the Netherlands and Germany among them. Keep a signed list of who received what and hand it to the bookkeeper.