I carry an envelope with about $50 worth of $1 bills on each trip. It's used for things like in the Amex lounge and housekeeping.

In my work brief I keep maybe $200 in mixed bills that I'm starting to realize I never use. The $1 bills I happily carry, the weight of them is never to the point where I'd want to stiff the people who help me or ask them for their Venmo address, which feels really insensitive or tone-deaf.