As seen the survivors will first arrive by truck, scramble for supplies, then get told they will be living together.
They will then begin their camp development, film some confessionals and then head to the first Challenge.
They will be wearing the same clothes from the truck, so I imagine it's later on the same day.

To start; split into gender challenge...
Manono:

Salani:

My belief is that all shots of the rope net/stair/ladder/balance beam challenge is all from Challenge #1.

1st Challenge
We start with Kat leading the challenge off for the women...

Notice all nine women there.

Then the ladies start to form a line.

Jump down half stairs into rope net.

Run down rope net to colored mat. Notice the edge of the Manono mat in bottom left corner.

(Possibly solve a puzzle or perhaps just wait for all tribemates to reach the mat before moving on.)

Climb up ladder to second staging area...

Notice the legs of the women survivors peeking through the space between the platforms.

Notice sabrina reaching up and kimberly looking over her shoulder down towards her.

Walk across balance beam...

Also on dry land are the shots of Greg with a slingshot and an excited cheer...



His buff is on his head in the first challenge, not for this one.

---

Now, we move into the water challenge(s).
Looks like we may have two challenges here as there is a water polo type challenge with survivor contact allowable AND another one involving a dutch-bucket race. Again, could be the same challenge, but I can't really figure out how they'd work together.
Anyways... It helps to have the full cast shot to identify some of the clothing.

Water-challenge shots with mixed gender (tribal colors and buffs noted).
Here we have, Kat in foreground (with female arm reaching towards her) and Sabrina in background. Sabrina looks to have a blue buff around her wrist. But hard to tell with that amount of blur.

Kat with Salani blue buff and ball, opposing female manono...

Blue buff around neck of Troyzan, whose holding down...

...Jonas with Manono buff.

Alicia running in water with Manono buff.

Michael? with orange buff. Around neck. and being held down by male with hairy chest? (Greg).

Notice the beard growth and is that a wedding ring? Maybe it's not Michael.

Colton being held down by 2 males, one right above him one to his left, but no buffs visible.

Also notice yet another male running into the frame from the right (in black-graphic shorts). I'm thinking 2 males against 2 males.

2nd Water Challenge?:
Monica falling off or jumping off tribal apparatus (walkway) into water at challenge.

Blue dutch bucket, denoting Salani. (Yet, I can't seem to figure out the clothing so I'm thinking perhaps dreamteamers) Still, shows 2 males and 1 female (at least) helping to move the bucket.

From the caps available looks like the tribal swap is set for a future episode (possibly ep.2) and will start to form as so...
Blue/Salani:
Kat
Sabrina
Troyzan
Monica
male
male

Orange/Manono:
Jonas
Alicia
Michael
female
male
male