I love doing stuff like this!
Set up a trail class and lead him through it. Expose him to a bridge, water, cones, poles on the ground, mail box, put on a slicker and take it off, drag something, etc.
If you don't have a bridge built, you can use a 4 x 8 sheet of plywood (ensure it's not slippery!) or a tarp staked down to walk across. The tarp can also be the "water".
The cones are set up so you can weave him through them, or back him up around them.
Set up the poles in a straight line, stagger them, raise one end a bit, mix them up each time and lead him over them so he doesn't anticipate the pattern. Set them up in an open L shape and back him through them. Set them up in a box and lead him in, turn him 180 degrees without stepping outside them and lead him out. When he's got that, turn him the full 360 degrees.
If he's good for you taking mail out of the mailbox, rig it up to squeak a bit when you open it and try him again. Get him used to the mail dropped on the ground.
To drag something, you hold the rope and walk beside him. You're actually dragging the items, but he sees it close to him, following him and gets used to it.
For a gate, if you don't have one, two standards with a rope between them will work.