Apparently even the default client has multiple hotbars, it's just one of those hidden features:
ido wrote:The official game client has 10 (!) hotbars with 10 cells each to take care of this. You can switch between them with a combination Alt+1, Alt+2, ..., Alt+0.
The lack of the drink button for me was the reason for switching to a custom client - the inability to quickly drink, especially in battle. But now the problem with fast water drink is completely solved.
1. Press Alt+0 to switch to Hotbar#0.
2. Add to hotbar every waterskin you have.
3. Place your waterskin to the inventory or to the belt. It doesn't matter where the waterskin is located, the only requirement it should be on hotbar.
4. Press Alt+1 to switch to your main hotbar.
5. From this moment you can forget about Hotbar#0 and drink water from all your waterskins using only one button with the new feature "Drink" at the main hotbar.
Enjoy.
Special thanks to the developers for this feature.
Bit clunky but with a one minute of setup time, potentially only once if you never unequip the belt/waterskins, you will basically have the desired drink button now.
EDIT: they also later changed the hotbelting from "whitelist" to "priority." Meaning that when you press "Drink" it will first check if you have any container on your hotbar with something to drink. If it finds one, it drinks from it. If not, it will check all your liquid containers using unspecified logic until it finds one or does not and gives "You have nothing on your hotbelt to drink." -message.