Cats that use litter boxes won't hold it in if there's no litter box. Although they are used to going to the toilet in the litter box, they may hold it in for a while if they can't find a litter box. But when they really can't hold it in anymore, they will find a suitable place to relieve themselves and won't hold it in forever. 
There is no substitute for cat litter.
1. Soil. Soil is the closest to cat litter in terms of feel, but you should choose a cleaner type of soil and clean it frequently, and do not use it for too long.
2. Waste paper. Tear absorbent waste paper into small strips to use as cat litter for your cat. You can also choose pee pads or cotton cloth.
3. Noodles. Noodles have good water absorption, but they are more troublesome to clean and can attract insects over time, so they cannot be used as a long-term substitute for cat litter.
