Fallout: The Lost Brotherhood
You may be familiar with the Fame system from PFS. Reputation is similar, but is based on your earned reputation + your charisma + other potential bonuses – any losses. Of course, you may buy anything that’s always available or that’s on your chronicle.
As far as ammunition goes, the most of one type you can have is equal to your 1/3 your level(rounded up), unless it is always available. I.E. if your level 3 you may have one box of 30.06 ammo. If you are level 4, you may have 2 boxes of 30.06. Often chronicle sheets will let you carry extra clips of ammunition. These are one (or more) time bonuses, and must be marked off when used.
Occasionally Reputation may be spent for bonuses. When spent in this way it is permanently lost, effecting what you can buy in the future. Check out Reputation Purchases for a full list of whats always available for purchase with reputation.
Regardless of your actual reputation, you can always purchase as if you had 1/2 your level off the available list. For instance, if you are a level 20 character with 0 reputation, you may still purchase as if you had 10 reputation, or 1461.