A 3 hour tour? Obviously you need a trunk full of money and a complete wardrobe for this kind of excursion! I don't see you as a Mrs. Howell type, so I'm guessing you'll be MaryAnn, or maybe Ginger?

I think the greatest risk would be a combination of the boat becoming disabled and someone going overboard and/or getting hurt in cold, rainy weather. Shock, hypothermia, bleeding and no communications.

I would suggest that each person bring extra sweatpants, hoody and socks in a dry bag or well-sealed trashbag, with some paracord attached to use as a tether if swimming is required. Even if you don't get wet, the extra insulation will be welcome in 3*C temperatures. If anyone requires prescription meds, tuck a couple day's worth supply in as well.

Building a fire can take time when its wet, which could be a problem if someone is shocky or hypothermic. I'd pack a good supply of chemical heat packs and mylar emergency sleeping bags or AMK Heatsheets Emergency Bivy Bags. These offer better wind and rain protection than just the mylar blankets.

I have nothing against TinderQuick, but I find that cotton balls coated with petroleum jelly work better and are less expensive. Carry them in an old 35mm film container (you might still find some at your local 1-hour photo processor).

I'd also bring several lightweight, woven, poly tarps, like REI and other outfitters sell as groundsheets for tents. The 8x10 ones REI sells are $6.50 each and weigh 18oz, 12x10 are $10 and 23oz, fold up pretty compact (at least when new). They may be cheaper at Walmart or Home Depot. Add some paracord and a folding saw to make shelter.

Lifeboat ration bars? 2400- or 3600-calories supplemented with vitamins and minerals, 5 year shelf life, compact, ready to eat. Though food probably isn't a big priority.

Handheld air horn for signaling?

I don't think carrying a PLB or SPOT would be a bad thing, though assuming you left info on your return time I think that its likely help would be rather quick to arrive either way after you missed your check-in time.