A nice steak dinner with vegetables, bread, and a trip to the salad bar will cost you like $15 or so. You can get a slightly less pricey meal but expect any good meal, breakfast, lunch, or dinner, to run you an average of $12 after tip.
Showers are free if you get fuel at that truck stop, otherwise they run about $10 to $12. You'll want to shower at the bigger truck stops though because the smaller ones either won't have showers or they tend to be a bit on the dirty side sometimes. The larger truck stops have very nice, very CLEAN individual shower rooms.
You won't have any problems with ‘em. The truck stop will supply clean towels and soap. All you need is a change of clothing and you're good to go.
Now procedures for fueling will vary greatly from company to company, and sometimes even from division to division within a company. For starters, you NEVER pay for fuel unless you own your own truck, which I desperately hope you won't attempt until you have some years under your belt.
Actually I hope you never attempt it, but that's a debate for another time. Your company will give you a fuel card which basically acts like a credit card. Some companies will let you fuel anywhere you want but most will have a list of approved fuel stops because they will negotiate better prices with certain truck stops. You will usually be able to buy some supplies for the truck with this card like oil and washer fluid also. That will be about it though.
The company card is not actually a credit card and will not work for purchases other than fuel and supplies at certain truck stops. But finding places for you to go to for fuel, a shower, and something to eat will be quite simple for you to figure out.
There are several books published which sell at most truck stops that will list most of the truck stops in the country in order either by interstate highway or by state.
So wherever you are you can just look in the book and it will tell you where all of the truck stops are on your route, how big they are, and what services they provide like 24 hour restaurant, 24 hour repair shop, check cashing, showers, etc.
By the time you are done with your training period your trainer will have shown you how to handle these everyday aspects of the road. It will be little or no concern to you by the time you are out on your own.
As far as sleeping goes, the beds in these trucks nowadays are quite comfortable. Most companies have trucks with sleepers you can stand up in and many of them even have bunk beds. I like to sleep on the bottom bunk and use the upper bunk for storage.
That's what most drivers do.