ItemLock allows you to lock items in your inventory.

A locked item can be configured to behave differently based on what you want:

You can have locked items become non-interactive in the vendor window so you don't accidentally sell your precious items.
You can have locked items' position be locked (so it is not moved around by bag sorting)
You can have items in your equipment sets be automatically locked.

Using ItemLock

Set a custom keybind (i.e. ALT-L) of your choice in Blizzard's keybinding menu under 'ItemLock' OR if you want to use click keybinds (i.e. Alt-Left-Click) configure this in /il config
Hover the cursor over any item in your inventory and press the keybind you set
The item should now be locked! Locked items will have a small lock icon in the bottom left (you can change the appearance of locked items in the config UI)
To unlock an item simply hover over it and press your keybind again.

Commands (/il can be replaced with /itemlock for any of the below)

/il - opens the configuration UI
/il list or /il ls - list out all items you have tracked to be locked
/il lock - locks the item the cursor is hovered over if it is currently unlocked, unlocks the item if it is already locked.
/il reset - unlock all items
/il version - display the current addon version

Notes/Disclaimer
This addon currently has support added for the following bags

Default Blizzard Bag UI (*)
Bagnon
Combuctor
ElvUI
LiteBag (*)
ArkInventory (*)
AdiBags (*)

Things may not work or explode if you are using any other bag addon as they all handle their frames a bit differently :).
(*) The position lock feature is currently not supported for these.