Some kind of visual distress signal is needed, both for day and night (but only if you boat at night). With kids around, I decided against the flare gun. I'm pretty certain a flashlight is sufficient for a night signal device, but someone else can confirm that. For day use, I have a distress flag (3x3 foot plastic flag orange with black square). These are only a few bucks, and can be clipped or taped or tied to a railing or bimini (or waved). You don't need a flag pole (unless you want one).
You also have to have an audible distress device. For the money (less than $10) you can't beat an air horn (a can of compressed air with a horn screwed to the top). These are a REALLY good idea if you ask me, as it is the loudest thing you can get for under $10. They sell them everywhere (Walmart has them). The horn that comes with the boat makes you legal, but it won't be heard over a stereo in a boat coming straight at you where the driver isn't paying attention. I keep it handy in one of the helm cup holders (the can of air fits perfect in a cup holder) so it is as quick to use as finding the switch for the factory horn.
You can't have enough ropes and fenders. The fenders that you can pump up (vs foam) are nice because you can keep the ones you don't use flattened out in a storage compartment. We have a half dozen hand pumps because they come with so many kids toys (basketball, volleyball, etc). Even if you only trailer and don't tie to a dock or other boats, you should have 4 of these. I use three on each side of my boat (with the valet service at the marina, I never know which side they are going to tie off to the dock with). And I keep two spares flat. I would suggest not going any smaller than the 6.5 inch ones. Anything smaller is too risky for something as big as a pontoon boat. Go even bigger if you have the room and need them (for example, if I kept my boat in a slip 24x7, I would get the 8 inch ones).
Vests, throwables, fire extinguishers were all mentioned above. An anchor is a great emergency item to have. If your boat stalls, it will keep the wind from causing you to drift.
I also carry a spare prop, hub kit, and the tools to change it.
