Are you going to barter the battery charger with the batteries or just sell some you have used and recharged? Little solar systems are an interesting thought. My worry would be that whoever you bartered with would be very excited to tell people you had extra solar to part with... just a thought.
Sugar was rationed until after the war, in 1947. Cooking oils may be hard to get, as soon as this year, but who knows... I thought about flour and yeast, but how many know what to do with it. Maybe those little lanterns you pull up? They come to about five bucks a piece, but light would be valuable, esp. by people on the road. Tarps could be good, for water trapment.
So which S.H.T.F circumstance hits us first...There are several in line...
Abigale, I kind of chopped up your post so I can respond to a few specific questions.
In my semi-rural area I know every face within a mile and most by name. With only a few exceptions I trust them to not attempt to steal from me. But still I would consider anybody who walked uninvited on the property to be a potential threat. "Keep out", ring bell at the end on the driveway." Keep in mind that there is a bit of a radio network between neighbors within 3/4 mile with small solar chargers. The neighbors are not a MAG. Every home is on it's own, some prep, some don't. But we do help each other out occasionally.
Small town a few miles away.
No trading or people who don't live on this property on the property. But if things are really bad I'm not walking into town either. Personally, I suspect with the exception of people coming out of the more urban areas this area should be relatively safe.
Considering the fact that SHTF may never happen and potential trade items can cost a of of money I try to focus of trade items I'd probably use myself in the future. I've got honeybees that I use about 150 lbs of sugar a year to stimulate early feeding with so keeping extra sugar works for me. I'll use it next year. I salt cure ham so having several years of extra salt plus another 100 lbs makes sense, especially considering that that salt and sugar will probably cost more next year.
We burn wood and use BIC lighters so they are worth keeping a few extra around although I've got to admit I keep a lot more BIC lighters than I'll probably ever use.
As far as solar goes I already use solar for much of my energy needs. But rechargeable batteries are expensive, both for the small stuff like AA for radios and larger batteries to power the well pump. I don't keep batteries for trade. But I do keep a few small inverters designed to run off a 12v car battery and solar charge controllers to properly charge 12v batteries. A friend a few miles away has lots solar panels they may be willing to trade for. I suspect they and I may be able to talk on the radio to facilitate a trade.
We've used Vegetable and Canola Oil and butter stored in the chest freezer for 3-5 years with great results but it is something we will always need, not a trade item. With the exception of the cost of the solar powered chest freezer that is a no cost prep. Possibly even a savings considering how fast the price is going up. But that requires a larger chest freezer, we went large when we got the last chest freezer.
Tarps are very useful. Probably not for trade but we always keep a few spares in different sizes.
hope this helps.