Buy Megabus tickets online as far in advance as possible if you want to go long distances in the UK. Tickets for Stagecoach bus can add up to a lot of money, and trains in the UK are some of the most expensive in Europe. Otherwise, Scotland is the best place in the UK to hitchhike, especially around the north and west coast. It might be your only option in really remote areas where buses don't even go. If you want to explore the many islands by ferry, fares for foot passengers can be surprisingly cheap. Look into buying an Island Hopper ticket if you want to see several islands.
Under the Scottish rights of access code, it is legal to camp almost anywhere you like without permission. You're supposed to camp out of sight of houses, so of course don't camp in people's gardens, and it is illegal to disturb livestock or damage crops when camping in fields. Fires are generally permitted, but keep them small and controlled.
Scotland has far more mountain bothies than anywhere else in the UK. Basically these are small cottages with fireplaces and minimal furniture that are open and free for anyone to sleep in for short periods. There are no bothies near towns or roads, so they are only practical if you are hiking in the area. Some are supplied with a small amount of wood or coal. Most are maintained by a charity called the Mountain Bothies Association; most of their bothies are listed at Mountainbothies.org. However, there are a large number of bothies maintained privately, which are not listed anywhere online. You must have an Ordinance Survey map to find these. Some are quite unpleasant, some are very clean and even have electricity!
You can find pictures of many bothies in the BBC story Bothy-bagging: Scotland's best-kept secrets revealed. In 2017, there was an article on 10 of the best wild camping sites in Scotland.
Scotland is a highly nomad-friendly country, with the ease of hitchhiking and legality of wild camping. The weather isn't really as bad as its reputation. As with everywhere in the United Kingdom, supermarkets like Tesco, Morrison's and Sainsbury's provide extremely cheap food.