Bad news is that there's no "the one" to get.
Goal Zero is the company/products that others are usually measured against. It's a good place to start looking, to get more familiar with what's out there.
While I don't have a specific product in mind, here's some good things to be aware of:
There are different types of panels, and some can work significantly better than others, especially in less than ideal situations, like overcast weather. Looking for backpacking equipment to use in Norway, this is pretty significant to me. It doesn't take a lot to slowly charge an 18650, and getting some juice can be a major upgrade from getting one.
You'd take a loss storing energy rather than charging directly, but for almost all cases, I think you're in the right path. Being able to spend more time actually capturing the energy, means you'd probably offset the loss.
Foldable panels (or some of them) can have weak parts that'll break with repeated usage. Quality here can vary widely between "flex film" type rollups, and cheaper Chinese foldable.
Some solutions allows you to connect multiple panels. That could give you the option of bringing one panel when backpacking, using two of them when car camping, and letting one be backup for the other.
For car usage, you also have the option of bringing your car battery into the mix. You could charge 18650s off of the car battery, let solar trickle charge it back up, and running your engine then becomes a nice backup energy source. There are panels made specifically for this, including easily connecting through the cigarette lighter type port, but some of those are "smart" these days, which might complicate things.
If you have the budget for it, it'd probably try to have that method as a separate solution, mostly for backup.
Charge controllers are important, although it can be hard to figure out how each one would perform in different situations.
Will it still deliver some juice in less than ideals situations, or would it shut down? Could it even drain the batteries when shut down?
One good sign to look for is MPPT - Maximum Power Point Tracking. Just like with batteries, if you pull too much amperage from a solar panel, the voltage will sag. Go too far, and the voltage would collapse to nothing, giving you zero energy. MPPT is about changing the load that the panel sees, to get the maximum amount of energy, rather than trying to pull too much amperage, and causing such a collapse. It can go "if I reduce the amperage a bit, I'll get higher voltage, and more energy in total, yay!".
There used to be an interesting company here:
http://www.aspectsolar.com
But they seem to have gone now. :-/
Oh, and portable solar is often based around either 5V (USB) or 12V (car batteries, 12V accessories). Some support one, some support both well, some support both badly. Worth keeping in mind.