UPDATED FOR 1.20.5 (24w12a and above!)

WEARABLE BANNERS
With this datapack you are now able to wear banners on you head (just like a pillager captain!). This feature has been in the game for a really long time but never usable in survival, now it is.
To get the banner on your head, just sneak 3 times (within 0.75 seconds or 15 game ticks) with a banner in your hand and it will go from your hand into your head slot. It will also make a little equipping sound to let you know you have put a banner on your head.
If you try this with banners in both hands, the mainhand will get priority.

Every time you sneak to equip a banner, you should hear a clicking sound to let you know you are equipping a banner on your head.

Switching Banners
If you want to switch banners from your hand to your head you now have to have one empty hand (doesn't matter which) and in the other hold the banner you want to put on your head
Then, just sneak 3 times and BAM! You have switched the banners :)
This works both when switching banners or when switching banners with other items equipped in your head slot (such as a Carved Pumpkin or a helmet).

Known Issues
None

If you have a suggestion you'd like added to the pack or something isn't working properly, please let me know.