Os benefícios da busca pelo recurso Natural Explorer do guarda florestal e pelo recurso Wanderer do fundo Outlander?

Rules As Written they provavelmente don't work together, so ask your GM

The rules on "Foraging" (DMG page 111) state:

Characters can gather food and water as the party travels at a normal or slow pace. A foraging character makes a Wisdom (Survival) check whenever you call for it, with the DC determined by the abundance of food and water in the region...

A foraging character finds nothing on a failed check. On a successful check, roll 1d6 + the character's Wisdom modifier to determine how much food (in pounds) the character finds, then repeat the roll for water (in gallons).

Certainly the Ranger's Natural Explorer feature would apply here:

When you forage, you find twice as much food as you normally would.

But the Outlander Background's Wanderer feature states:

In addition, you can find food and fresh water for yourself and five other people each day, provided that the land offers berries, small game, water, and so forth.

The question now is "Does the Wanderer feature count as foraging?"

Foraging is defined (and only mentioned) in sections talking about things to do while viagens. The Wanderer feature, however, has no such restriction, in fact, it never mentions a time-requirement or anything of the sort. Like many background features, it is not a very defined ability in terms of the game-rules.

Though searching for food is certainly similar to the common English sense of the word "forage" the DMG specifically defines the process of foraging and it does not seem that the Outlander's feature follows these same rules, so I would say it is does não count as foraging.

Ultimately, there aren't rules set forth for how the Wanderer's food finding ability works, it seems like it apenas acontece whereas foraging, as defined in the rules, involves a Wisdom (Survival) check.

The Wanderer feature does not follow the same rules as foraging (or really any rules) so it would be up to your GM to decide whether it counts as foraging

Yes. The outlander can find food for 6 "normally" so a natural explorer doubles that to 12.

That would be a plain reading of the descriptions given.

Provavelmente não, mas pergunte ao seu mestre.

In 5th Edition, similar effects don't tend to stack.

Combining Spells:

The effects of the same spell cast multiple times don't combine, however.

Temporary Hit Points:

If you have temporary hit points and receive more of them, you decide whether to keep the ones you have or to gain the new ones.

Resistência:

Multiple instances of resistance or vulnerability that affect the same damage type count as only one instance.

There isn't a rule specifically dealing with the interaction between the Outlander background and Ranger's Natural Explorer ability but, using the precedents set above, it would be logical to conclude they are not meant to stack.

But this is interpretation of intent, not rules as written, so consult with the DM to see how s/he wants to play it.