Well, my idea would be that there would be some items in the kit that they would use just for that weekend and that would compel them to take it on the boat, and some of them would be fun items, and then there would be some items that they would keep in the kit for future use...

Here's a few ideas in addition to the items you already listed....

• a map of the lake with depth soundings, boat ramps, marinas and marked with the location of the house you're staying at (free if you print them yourself?)
• Sunscreen packets from minimus.biz or similar - less than $1
• Sunburn cream packets - same as above - less than $1
• bug repellent wipes - same as above - less than $1
• soap for fishy hands or towelette packets - same as above - less than $1
• one hand warmer - you could get the "toe" size that are real small. - less than $1
• Leland Marine Emergency Strobe Light - $15
• liquid filled 20mm button compass $4
• Coghlan's Compass and thermometer zipper pull $3
• Lightload Towels - super compressed towel pack minimus.biz $1
• 1/8"x2" ferro rod - $1 at goinggear.com
• P38 for a ferro rod striker - $1 - or use a cut down hacksaw blade which is even cheaper
• one lure - get one that would be appropriate for the lake you're visiting - get something cool and colorful - $3
• hemostatic Kelly forceps 5.5 inch - cheap ones for pulling hooks - $1 at bpmedicalsupplies.com
• small fingernail clippers and lanyard for nipping fish line knots - less than $1 at dollar store
• cheap sunglasses - all matching so y'all can look alike for the pictures - $1 at dollar store
• a printout of the fishing regs in very small print - perhaps on a business card sized paper - It would show sizes and bag limits for the most popular species you are likely to catch - print it yourself so it's free - include the year so people will throw it away after this season.
• keychain mini measuring tape - something to measure fish with - $2
• one coffee stirrer, two creamer packets, two sugar packets - free - snarf from coffee shop
• Aqua-Pouch 1 liter - $6 from bepreparedtosurvive.com
• moleskin - for blisters from paddling - $1
• Lansky mini crock keychain knife sharpener AND hook sharpener - $2
• 4" glow stick - $1
• fish stringer - $1
• Salt, pepper, lemon juice packets - fixin's for a shore lunch - packets at minimus.biz for less than $1 Throw in 1 or 2 square feet of foil.
• An empty mini-ziplock that is sized perfectly to the size of your fishing license.
• small carabiner attached to the carry bag OR a small carabiner plus a keychain float to make the entire bag unsinkable - $2 to $3
• microdropper bottle of reel oil - buy microdropper bottles and fill them yourself - $2
• netknots.com knot cards - 2-1/4"x3-1/2" - $6

I think the digital camera bag is fine. An altoids tin may last longer though and might even be cheaper. You can get plain tins from places like bepreparedtosurvive.com. You could also wrap a hard sided tin in paracord. My personal favorite for what you're trying to do would be an Equinox No-See-Um Mesh Bag. They come in three sizes and they are cheap (between $3 and $5) They are also very high quality with a nice cord lock on them and they are see through. http://www.equinoxltd.com/the-gear/bags-and-pouches/no-see-um-mesh-bag.cfm If you went with the mesh bag, then you could use Aloksak baggies or just cheap mini ziplock baggies for the contents. You could have a baggie for first aid, a baggie for condiments, etc.

Also, I don't personally believe in using ponchos on boats. People who fall into the water while wearing a poncho can end up with the poncho around their head, and once they get that squared away, they try to tread water and swim with it and it is very hard to do. In a panicked state, people don't think to just slip out of the poncho and abandon it - they keep it on and struggle. I'm not sure what you could replace it with though. You could look for a Tyvek rain jacket or look for something called a "marathon jacket" - jackets that are waterproof and given out to marathoners and are disposable... check out http://sheddableshell.com/ The only problem with jackets instead of ponchos is that you'll have to decide what sizes to buy in advance.

What a cool idea. I hope I came up with some good ideas for you.