Dang it Doomonkey and Clockturn! I was about to suggest a backpack idea yesterday, but I got busy and didn't get a chance.
Inventory systems should be changed up to make everything a bit more realistic.
Instead of the 5 slots players have now, it should be downsized to 3. For the rest of the post, I'll explain in pictures.
This is our basic player with the new standard inventory. He decided that he wants to cut down some logs.
After cutting down a tree, a log is added to his inventory.
He decides he is going to chop down another tree.
After cutting it down, another log is added. Now his inventory is full and he can't get anything else.
Let's retry at situation now with a backpack item.
The player would like to cut down a tree.
After cutting it down, the log is then added as a variable to his backpack.
Backpacks are used to hold items for a player when they normally wouldn't have room. They are controlled by slash-commands (Which could easily be turned into a GUI).
/openpack lists the contents of the backpack (This could be a keybind to open the GUI)
/putaway itemname moves an item from the inventory to backpack (GUI interface to do all this)
/takeout itemname moves an item from the backpack to the inventory
/remove itemname drops an item from your backpack (Inventory dropping would still work with ctrl+w)
/switch itemname1 itemname2 switches an item in your inventory (1) with an item in your backpack (2)
/setinvdefault makes it so that items that are picked up go into the inventory first if there is room
/setbpdefault makes it so that items that are picked up go into the backpack first if there is room
There can be different sizes of backpacks that the player can buy that would allow them to carry more stuff, but would also make the player move slower.
Also, the reason I chose 3 slots instead of 6 because of this system. 2 weapons or tools will be easily accessible by the player for quick usage. Any other tools or weapons the player might need could be kept in the inventory.