First off, while I do not own the Age of Rebellion core rulebook, I own both the Edge of the Empire (EotE) and the Force and Destiny (FaD) core rulebooks. Since the system is pretty much the same, what I found in these books should apply to your case, unless Age of Rebellion has specific rules for hunger.
The books I own don't give clear uses for rations, besides staving off hunger. Going without food or rations calls for a Resilience check (the difficulty depends on the environment and is at the GM's discretion). The consequences of failing such checks are also left to the GM. You can also try to forage for food with a Survival check (again, it depends on the environment). The importance of food depends on the GM, and can be anywhere from essential to cosmetic. I experimented a bit with hunger and food in my long-running game (see below).
The only time (as far as I know) that starvation is mentionned (in both EotE and FaD) is under the Resilience skill. It says that the skill can be used to protect a character against the effects of malnutrition or dehydration. As such, it's up to the GM to decide if thirst and hunger should be important. If your game is about a group of stranded Rebel operatives that struggle for survival on a hostile world, food would be far more important than if it is about, say, infiltration in a major city.
I would also note that, since ships hold food (but I would say not travel-ready rations, think Star Wars VII blue powdered foodstuff) for months at a time, hunger should not be a problem most of the time.
In my game, I don't give food a big importance, unless the players do not have an easy access to it. For instance, they had to go for a whole day without food or water after being stranded, so I had them play a Resilience check for each meal skipped. If they failed the roll, they suffered a Wound, plus 1 Strain per Failure. Threat added a Setback dice on their next roll, while Advantages added a Boost dice. I was an Easy (1) roll, but it would have been more difficult if they hadn't been on a temperate, verdant planet.
What I suggest
- Use rations as a need: They set out for the wild? Make sure they know that if they don't bring enough food, they will starve and have to play Resilience checks (unless they can scrounge up some food using Survival), with harsher environments making for harder checks. I do this when they leave their ship behind to explore.
- Use rations as a tool: You can consider they always have access to some food, and have good food give them bonuses. It could be Strain recovery, a Boost dice on a strain recovery check, or a Boost dice on future checks (didn't test that one out, but I would see that work out, say, at a state dinner with a diplomat that needs some convincing to join the Rebellion). I did this when my players braved a snowstorm and got themselves a nice, warm meal.
- Handwave rations: Maybe rations aren't that important to you as a GM. Maybe the Rebellion always gives you players plenty of rations for their missions, or maybe they always have food sources nearby. Whatever the case, you don't need to give rations any importance at all. This option makes Survival less useful though. I tend to handwave food most of the time, because they rarely stray from civilizations, being Smugglers and such.
If you still run the Beginner's Box adventure, I would say it depends on what happens there: the EotE beginner's box adventure spreads over two hours (in-game time), so I wouldn't bother with it. However, if the AoR adventure spans more time (or if you plan on continuing the story after completing the adventure), managing food can add a little something to their struggles.