Traditionally, the minimal “bath bag” was the toothbrush. On the other hand some people carry shampoos, lotions, potions etc. and as soon as you carry a liquid you need to go through the security theatre of putting liquids in a see-though bag etc.
My bath bag has served me well for a few years now. I operate on the basis that shampoo will be available on a trip, that I avoid liquids so I don’t show anything at security, and that any medical items / drugs need only to last until you can get to a drugstore for more supplies. Here we are:
First of all, the bathbag is actually a pencil-case. A shaver is kept in one compartment, avoiding bristle spread. Drugs are kept in another – which is hardly ever opened. The main area is what is normally opened in a hotel.
Main items: Toothbrush, toothpaste, battery-shaver, wet shaver (can be used dry!), nailclipper, earplugs.
Potions for dry atmosphere: Clarins mosture balm (free sample size), Clarins lip protector.
Drugs to deal with symptoms of illness: 2 sachets lemon flu relief (Paracetamol+Nose clearer), Dequadin throat anasthetic/antibacterial, Ibuprofen Meltlets, Loratadine anti-histamine, Boots 1hr Anti-Diarrhea, Tums stomach treatment, Vick inhaler. 1 a day Asprin micro-dose (not shown).
The Braun 350 battery shaver woudl ideally be replaced by a (micro)usb rechargeable unit to avoid needing to change AA batteries every few months.
I found that the moisturiser does deal with dry lips, but it tastes bad, so I need to carry lip treatment.