In a previous post, I mentioned some variations for farmer's walk loading - basically, change what you carry.
Waiter's Walks - Carry the load like a waiter carrying a tray - one hand, up at shoulder level. You can also carry it locked overhead. Locked overhead will make for a less stable weight, but held near (not on) the shoulder makes for tired arms! Almost always unilateral.
Shouldering Walks - Get the weight up on the shoulders and walk with it. Great with sandbags, miserable with everything else.
Unilateral Walks - Carry one weighted implement (barbell, dumbbell, kettlebell, whatever). Alternate sides each trip, or live-hand swap them at the mid-point (i.e. don't put it down, just hand it off to the other hand). Great for core stabilization - you really need to work overtime to keep the weight from pulling you off-balance.
Lopsided Walks - Carry two different weights in either hand. You can also mix implements - carrying a 32kg kettlebell in one hand and a 50 pound sandbag in the other, say. You can do this with shouldering, too - sandbag over one shoulder, something else carried in the other hand.
Grip-centric walks - Carry thick-handled implements, carry hex dumbbells by the hex (no fingers on the numbers, that's cheating), carry two weight plates pinch-gripped in each hand, carrying weights with finger loops instead of in the palm of the hand, etc. Anything that makes the grip the most likely thing to fail!
Those are just a few variations I use.