The point of a going-out bag is to carry less. That only works if the less is the right less, and the way to get there is to decide once and stop deciding every time you leave the house.
The five that always go
Phone. Charged before you leave, because a small bag has no room for a power bank.
Cards. One debit or credit card, one ID. In a card holder, not a wallet.
Cash. Twenty dollars folded flat behind the cards. Card readers go down, coat checks want cash, and a card is useless in both cases.
One key. The door key, on a small ring. Not the full keyring.
Lip. One product. The one you are already wearing.
That is the load a small bag is built for and it closes comfortably with room to spare.
The three that are worth the space, sometimes
Blotting papers or a compact. Flat, light, and the thing people actually reach for at hour three.
Two pain relievers in a tiny tin. Takes almost no room. Worth it.
Hair tie. Around the strap clip rather than inside the bag, where it disappears.
What to leave
Full makeup bag. Sunglasses, if it is night. Notebook. Second phone. Charger and cable. Water bottle. Anything you are carrying "just in case" that you have not needed on the last five nights out.
The just-in-case items are what turn a small bag into an argument with a zipper. If you genuinely need a charger, that is a different bag or a jacket pocket.
Do the packing the day before
Load the card holder, put the key on its ring, put both in the bag, and leave it packed. The reason people abandon a small bag is not size, it is the ten-minute transfer from the everyday bag while already running late.
A going-out bag that lives permanently loaded with cards, cash and a key gets used. One that requires unpacking your daily bag first gets skipped.
Pack for how you will carry it
If you will be dancing or standing all night, everything hard goes in the interior pocket so it is not pressing against your body through the panel. If you will be sitting at a table, it matters less.
Heavier items sit lowest and closest to your body. A bag loaded front-heavy tips forward on the strap and the flap or zip ends up facing out, which is exactly what you do not want in a crowd.
Security, briefly
Zip closed, bag in front of your body rather than behind your hip, strap over your coat not under it. In a crowded room, hand resting on the bag is enough. That is genuinely the whole list.
A bag worn behind the hip in a crowd is out of your sight and out of your reach at the same time, which is the only real mistake in this category.
Getting home
Unload the bag the same night if you can, at least the lip product. Anything with oil in it that sits in a lined bag for a week will eventually leak into the lining, and lining stains do not come out of a light-colored bag.
Then stuff it lightly with tissue and lay it flat. A soft bag stored empty and folded holds the fold. Ours ships flat for exactly that reason, and the same trick that fixes it out of the box keeps it in shape between nights.
The one-line version
Phone, cards, twenty dollars, one key, one lip product. Packed the day before. Everything else is optional and most of it is not worth the room.