My son loves to draw and the aquadoodle mat is great for doing lots of drawing and scribbling without any mess, paper, crayons etc. You just fill the pen up with water and they can start drawing on the mat.
They can draw over and over again too. As the water dries, the picture disappears meaning they can start over again next time. The outside of the mat has lots of letters to trace too - which helps with fine motor skills and learning letters. At the moment it's available on amazon for £13.99 reduced from £19.99 and the reviews on the site are very good.
Games for 3 Year Old Boys
Gator golf is a great fun game for 3 year olds. You have to putt the golf ball in the gators mouth and then he'll use his tail to toss it back to you. It's currently reduced from £15.99 to £9.99
Another great simple game is Pop Up Pirate. Take it in turn to put swords into the barrell to see who can make the pirate pop up. There's a couple of pounds discounted from this game.