Still new to the game. If you have more than 1 "before combat" option, such as the hero's ability, allies' ability, item(s), etc, how many can you use?

Thanks in advance.

according to the rule book you may use each of your hero's and allies before combat abilities once each and you may "activate" one item with a before combat ability. If an item is a discard or an always on, there are no limitations, so up to one hero ability, one for each ally, one activate-to-use item and any discard to use items.

Before Combat
Many Challenges, Heroes, Items, and Allies have “Before
Combat” effects and abilities. These effects are resolved before
the first round of combat begins. When you draw an adventure
card with a “Before Combat” ability, you must resolve that ability
first—even before using any of your own “Before
Combat” special abilities.
Note that between your Hero, Allies, and Items, it is possible to
have multiple “Before Combat” special abilities. After resolving
the adventure card’s “Before Combat” text, you may use each
of your Hero’s and Allies’ “Before Combat” abilities once.
You may also activate a single Item with a “Before Combat”
effect. However, you may use these abilities and effects in any
order you desire.

You may activate a single card during your
movement step and a single card during your
market step. During the adventure step, you may
activate a single card “Before Combat” and a single
card during each round of combat (see below).
Note that “Always-On” and “Discard” Item cards need
not be activated and therefore do not count towards these
activation limitations.

This is all straight from the rulebook

ok, so if I have 2 items with before combat ability, I should keep the best one and sell/trade the other one, correct?

If they are both activate-to-use, yes, unless you want the versatility or in case you get knocked out, you can still have at least one. Or if one has a good always-on ability as well