I've always used snow, when in the snow. It is kind of better than water because you don't get that wet and it does wipe. You do have to consider when the snow melts though, pick somewhere that is fair distance from a creek or river so that it can have time to filter. I have spent much time in SE Asia using mandi - most commonly like a small plastic pot of water and your left hand. It's an ancient custom and would have been fine when populations weren't so dense, or rural areas where your hands would soon be scrubbed clean from physical work. Also, the mandi came about in much warmer climes and traditionally sarong wearing populations and much different diet. The world has changed. 30 years ago it was common to see a group of women up to their breasts in a river all talking to each other while they were having a poo. Our populations are too great for that now. I also remember a huge road house for trucks and busses - it was on a lake. The toilets were over the lake - fish would be waiting eagerly underneath. Guess what was on the menu

Shitting in rice paddies was also common practice as a win win.
I carry toilet paper with me now and dig a bit of a hole. Toilet paper is an eye sore but breaks down quickly even in a shallow hole. I always try to go somewhere that is unlikely to be walked which is usually very easy where I go - and also somewhere that won't run into a water source. I used to use leaves and grasses - most leaves are like magazine paper

, and most grasses in the bush are dry and hardy

; bits and pieces usually come out in the shower

. Mosses are awesome, but very slow growing here - so I don't use them. I too have been giving this some thought, more for at home though. As an aside, we usually keep about a two week supply of everything - kind of prepper mentality. As a backup we have a box of Scott Essential Jumbo Toilet Tissue Roll - 8 Pack (2400m of Tissue). They're meant for those toilet roll holders that you see in some public toilets. I think we got it at bunnings. It doesn't take up much space and should last a long time. We've had it for a couple of years not having to use it yet. I still hope to hear some good ideas for alternatives though