Everything I know about this I learned by having it go wrong in a nightclub toilet at half past midnight. The good news is that the fixes are mostly about doing less rather than buying more, which is not what anyone selling setting spray would like you to hear.
Less base, not more
The single biggest cause of makeup sliding off is putting too much on. A thick layer of foundation has nowhere to go as your skin warms up and moves, so it breaks apart and slides into every line you have. A thin layer, built up only where you actually want coverage, will still be there hours later.
So: a small amount over the whole face, then a second pass with a tiny bit more on the two or three places that need it. Concealer only where there is something to conceal, rather than as a second foundation. This sounds obvious and almost nobody does it, myself included for years.
Powder only where you actually get shiny, which for most people is a strip down the centre of the face. Powdering everywhere is what makes skin look flat under a phone flash, which is the exact lighting condition your night out is going to be documented in.
The wing, and why yours takes four attempts
Because you are perfecting one eye and then trying to match it, which is impossible. Faces are not symmetrical, and a wing that is technically identical will still look wrong because the eyes underneath it are not. Correcting the second one against the first is a game you cannot win.
Do both roughly first. Two light lines, no pressure, nothing committed. Then look at them together and correct them towards each other. You are not aiming for identical, you are aiming for a pair that read as matching from a normal distance, which is a much easier target and the one everyone whose liner you admire is actually hitting.
The tool that does the most work is a cotton bud with a little micellar water on it. Sharpening the edge afterwards is how the clean version gets made. Nobody draws it perfectly. They tidy it perfectly, which is a completely different skill and a much more learnable one.
What is actually in the bag
Lip liner, because lipstick goes and liner stays, and a lined lip that has faded still looks intentional. Blotting papers rather than powder, because layering more product onto a face that has been out for four hours is what creates the thing you are trying to prevent. A spare hair clip. That is genuinely most of it.
Not in the bag: foundation, a full palette, or anything requiring a mirror and good lighting to apply. You will not do it. Nobody has ever successfully rebuilt a base in a club toilet, and the attempt always looks worse than the honest four-hours-in face did.
Setting spray goes on before you leave, in a proper fine mist held at arm's length, not three wet blasts at close range which just dissolves what you have done. It is the last step and it does help. It is not a substitute for a thin base.
The stuff that photographs badly
Anything with SPF in it, under a flash, will reflect white and make you look grey. This catches everybody out and there is no fixing it afterwards. If a night out is going to be photographed, keep the SPF for daytime and use a base without it.
Heavy glitter migrates. It will be beautiful for two hours and on your cheekbones by four. If you want it, put it somewhere it can migrate attractively, and accept the timeline rather than fighting it.
And very matte everything reads as flat and older on camera, especially in a dark room with a hard flash. Leaving a bit of natural texture and shine on the high points is what makes skin look like skin. The fully-blurred look works in daylight on a phone screen and almost nowhere else.
Thin base, powder only where it shifts, both wings roughly then corrected together, liner over lipstick, blot rather than reapply. None of it costs anything and all of it works better than the fourth setting spray you were about to buy.
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