Many YouTubers use gaming mice with special buttons, such as the Razer Naga and Razer Deathadder.
I have the Razer Deathadder, and the side buttons look like this:
http://gyazo.com/907e1bd3145315058f9cf6a2dcae6863
It's rather useful for easy switching.
Before I got my Razer mouse, I managed to get decently good at it by doing this:
I had 1 as Sword, 2 as Bow, 3 as Fishing Rod. (Inventory slots)
I would start on Sword and scroll down two slots to my fishing rod. (I had a mouse that clicks every slot it scrolls.) I would then right click once to cast the fishing rod, then reach my left hand up and tap the 1 button right afterwards to switch back to my sword. I also did a similar thing for Flint and Steel.
This worked for me in the past, and I see no reason why it shouldn't currently, unless you have your Sprint key set to something unusual or something like that.