When I get around to it I'm going to cut up some old towels and do some home sewn baby wipes. You can buy them from many SAHM on the internet for about 50c to $1 each, and they make a great alternative to disposable ones. And you wont get them muddles with normal face washers.
Try a couple of different varieties to find out what works best for you. Polar fleece on one side, flannel or towelling on the other. Use one side to wipe the poo away, and the other to clean up.
You could either wet them and carry them in a zip lock bag, or you can make a solution in a small spray bottle and carry it with you - very similar to the recipe Kathryn mentioned
The internet is a great tool for finding this sort of stuff out.

I also made all my own bunny rugs from flannelette - the best thing is you can make them what size you want, and they can double as sheets.

You can also save heaps of money if you knit by buying second hand jumpers and things from the sallies and pulling them apart - then reusing the wool to make something you like! $2 for wool rather than $30 is a big saving.

Fi