I have never forgotten, nor have I wanted for, anything on a solo self support, with the exception of more days on the river. Think of your adventure as a trip to the moon – on gossamer wings, just one of those things…
First and foremost, don’t bring anything you won’t be using. Think multiple use wherever possible. Here’s my advice to organizing gear for transport to the river. Use some kind of accounting system for everything you will use on river. Make a checklist. Here is my list, renovated and updated many times over the years. Yours will likely not consist of the identical items as mine, but should otherwise include items of similar function, if not form. Listed brand names are not endorsements, but rather personal reminders of what specific gear has worked successfully for me in the past, so I know exactly what to grab in the heat of battle (i.e., the short amount of time sometimes occurring between procuring a permit and launch date). I keep a bag of kayak self support gear available just for such occasions.
Some items on my list are no longer carried, but I have left them to remind myself to seek other alternatives. One example is the vestigial candle lantern. I no longer carry it, preferring a similar sized and weight battery operated area light, but the thought of its flickering, warm incandescent glow on a cool night without a fire still gives me pause when packing. Even the area light is far from necessary. For the most part, it is a luxury obviated by a good headlamp. Even a headlamp can become a serviceable area light by shining it up through a opaque filled water bottle. When I began kayaking, good headlamps were poorly collimated incandescents, rarely more than water resistant, requiring extra battery reserves. Today’s LEDs ensure good lighting of all types for weeks at a time. Their beams and waterproofness are reliable enough to get you downriver if benighted, or reveal the source of that terrifying racket at the far end of your lonely sandbar on a moonless night as an industrious beaver or playful otter, wanting nothing whatsoever to do with you.
It may be impractical, and equally inadvisable to actually pack your boat before arriving at the launch site. It will be way too heavy to get up to a roof rack, and possibly exceed rack limits when combined with other boats and gear. You can add to that the oven style baking in the sun of the contents of your boat while in transit. However, if trailering boats, pre-packing stow floats into the kayak may be a reasonable approach, if the put-in trail isn’t too arduous.
Don’t check anything off the list until it is actually packed. It is far too easy to leave behind some necessary piece of gear you think you’ve packed. Resist any temptation to upset the applecart by opening a packed river bag in order to confirm if something was indeed packed. This is the reason for rigorous adherence to the checklist regimen. If it got checked off, it is in the bag. Stow floats may be the integrated solution for packing, if there is adequate room in the transport vehicles and they are robust enough to survive the rigors of out–of boat handling. I won’t risk that. The stow floats go into my river bags along with everything else going into my kayak. A fresh, unmarked checklist goes into the travel bag(s) as well. I generally end up with three separate packed bags traveling inside the vehicle: one for all gear going into the boat, one for food, and a third only for on-river paddling gear. If any food items need refrigeration, I make a note of it, perhaps on the fresh checklist, and stick it in the top of the food bag so they will be remembered to be pulled from the ice chest when packing the boat at launch. It is often surprising how cool items can be kept within your boat near the bottom of the hull, within snowmelt watersheds.
The river launch site, while not optimum, will almost certainly be the last opportunity, if at all, to replace any forgotten or broken gear once on river. I use the fresh copy of my checklist to check everything into my stow floats and kayak as I load them. At this point I am as sure as possible that everything intended for my trip is going with me.