Sawdust, peat moss (very cheap, when you buy a huge brick of it), shredded newspaper -- there are many options.
The main point of odor control is to simply prevent air from drifting over the source of the offensive odor. You'd be surprised how well this works. That's why flush toilets are much less smelly than an outhouse.
To a lesser degree, you also want something that will complement the high-nitrogen content of dung, when it comes time to compost it later. You know the "browns" and "greens" ratio of composting? Well, ironically, dung goes into the "green" category. You need paper/wood/leaf products to balance it out, to aid in composting.
I'm going to be earthy here: when you're on the toilet, you're NOT smelling the human waste under inches of water. You're smelling seconds or minutes ago, *when it was surrounded by air* and also the residue it left behind on YOU.
I've tried the 5 gallon bucket with peat moss technique. It works. I'm not just reporting what I've read; I actually tried it, for several weeks. I got one of those special toilet seats that fits on a 5-gal. bucket. It's a great prep to have. I also got a brick of peat moss. A thin layer of peat moss sprinkled over "your business" does indeed turn off the smell like flipping a switch.
Of all the areas of "survivalism", my family is about 10/10 in "waste management". We have 2 leach fields that don't require electricity -- the old style anaerobic septic system. All we need is some greywater, rainwater, pondwater to manually put in the toilet tanks, and we can continue to flush toilets as normal! I wish we were as well-prepped in every other area...