This weekend I will be fishing with a friend of a friend. We will be fishing the Delaware River. Im fairly positive that he owns a bass boat and will also be fishing with his dad, making at least three people in the boat. This will be my first time in this situation. Looking for general advice and specific stuff too. I plan on bringing 6 rods, 1 tackle backpack, and a soft plastics bag. I will also bring a lifejacket and money for launch fees and gas. What Else do I need or need to know?

I personally wouldn't bring that many rods. I'd limit myself down to 3 maybe 4 max. I don't want to flood someone elses boat with all my crap. 

I fish 3 out of a boat a lot

 

Each person must be aware of each other before casting!

Etiquette as a guest in a boat is 5 rods or less and 1 bag.

Ask the boat owner BEFORE you load your gear how many rods he wants you to bring. He may not feel the same as the people who post here. His opinion is the only one that matters.

definitely wear sunglasses in close quarters like that.  some people have bad spatial awareness

He may already have an extra lifejacket for you. I would ask your friend if that is the case.

I will already have one ready for guests on my boat.

Have fun . 

Use diffrent presentations then the other two fishermen this should help you catch the fish your fellow Anglers are missing. do your best to avoid Crossing Lines offering to provide some gas for the tow vehicle or Beverages and lunch is a great idea.

How impolite is it to outfish everybody else in the boat?

 

Do it anyway!

Sounds like you have a good game plan. I love that you are contributing money for launch and gas. Don't love the 6 rods part though. I would bring 2.