Floating Boxes
Start with SpongeBob and push the two wood boxes into the water along yellow arrows to form bridges and push the purple button. Now have Patrick build longer bridges, first by pushing the two wood boxes along the green arrows, then by pushing the three wood boxes along the three red arrows in the indicated order. Step on the green arrow to free SpongeBob.
To collect only the Krabby Patties, simply push the remaining two boxes down to build a bridge to the island in the corner.
To collect Krabby Patties AND Bonus Bubbles, you need to learn a few fancier moves. Place SpongeBob at position "A", then have Patrick move the first wood box in front of him (along the blue arrow). Now move Patrick to position "B". Switch to SpongeBob, who can now push the box left and away from the wall. Push the box all the way to just below Patrick. Switch back to Patrick and build a bridge at position "C". Collect Bonus Bubbles, and repeat this process with the second box to build a bridge at position "D".