I have noticed that I have gotten two of the same questions regarding Sword and Backpack from people new the to the game and that style of game. The first question is;
What about all of the other classes such as the Ranger, Cleric, Warlock, Monk, etc?
In Sword and Backpack, additional classes are not needed for two reasons. The first one being is that all of these additional classes are just specializations of the core classes with different flavor and flare. The difference between a Wizard, Warlock, and Sorcerer is their origin of magic and their backgrounds. Same goes with the Fighter/Cleric/Ranger/Monk and the Rogue/Assassin/etc. This leads me into the second reason which is the different abilities of these classes. Once you start adding in all kinds of class specific abilities you start to lose the soul and the whole point of Sword and Backpack.
What about all of the different races?
Outside of different numeric bonuses and various abilities races are about flavor, culture, and background. For Sword and Backpack, there is already a heavy stacked bonus right out of the gate so adding anything numerical would push things into the ridiculous range. Adding various abilities would also defeat the purpose of Sword and Backpack for its easy of use and story focus (the power and draw in my opinion is the great player agency and fiction). So, if your campaign wants to include races other then human, it is a fiction and flavor point. There does not need to be any mechanic benefit or detriment to being one of the many fantastical races out there.
This brings me to Professions in Sword and Backpack...
I have always been a fan of giving characters motivation and things to do outside of combat, treasure hunting, dungeon delving, etc. This types of things also give them unique skill sets to solve various problems they come across. An example of this is in one of the games I was in, the character decided that she used to be a midwife and during the course of an adventure delivered some babies, tended to pregnant women, and saved some lives. Some of this led to some interesting story hooks and the party was off on a side adventure. Giving characters a profession gives them more depth and shows what their life was like before becoming an adventurer.
Mechanically speaking, any use of skills that would fall under this profession that would require a roll would get the class bonus of +5 and the character would have a kit (various tools, a few simple supplies, etc) to help them in their profession. Simple as that. There are a lot of games that have tables of "failed professions" and there are a lot of those lists that can be found online as well. I will point you to a list of Medieval European Professions that should give you some ideas.
Adding these professions to a Sword and Backpack game also has the bonus of creating some of the classes that are not in the game. You have a player that wants to be a holy warrior with healing skills (a Cleric)? That player should be encouraged to be a Fighter with some type of medical profession related to a Religious order.