As has been said, start somewhere.
I have both panniers and a BOB trailer.
If I am going for a trip and expect to see wild life, I put my camera equipment in the trailer, inside a water tight bag with lots of protection for the camera and lenses.
Otherwise, I prefer panniers.
Borrow some panniers. DON'T buy the cheapest ones you find in the catelogue. Go for a few rides. This will give you a hint regarding what you need.
I was amazed at how much water I needed. I thought two 28 ounce bottles that the bike carries was going to be more than adequate.
Now I carry almost a gallon, for short rides. If I am going on a long ride, I fill up a 10 Liter MSR bag and take it with me.
Trailer. Borrow one and try it.
My wife like the Jandd Panniers. She has her stuff on separate bags stored in the Jandds.
I wore out a set of Cannondale panniers over the years. I loved them because they have gobs of pockets to store things in their own pockets. I now have Arkel bags. These are even bigger with lots of storage spaces. Thus, when I want my water filter, it is in it's own compartment. When I want my tent stakes, they are in their compartment. Food, stove, clothing, etc are likewise in their own spaces.
So, go for a short ride and find out what you need.
Additionally, I carry two spare tubes, patches, 8 CO2 cartridges, tire pump, set of hex wrenches, three spare spokes, spoke tool. I even have a bottom bracket wrench in one of my panniers.
I carry a full bottle of Advil, spare riding gloves, pair of warm gloves, a head/neck covering for cold mornings, three or four tee shirts, down vest, extra socks, long pants (gortex), Gortex Jacket with zippered arms and lots of pockets.
I also have learned to have a packing list in my handle bar bag so I can make sure I have everything for the trip.
Money, credit card, tincture of iodine (for cuts,etc) Ace Bandage, stapler (got from the local ER doc)= great for closing bigger cuts.
I also carry a roll of black electrical tape. Handier than duct tape - on my bike anyway.
Many people think I travel overloaded. However, the only recent trip that was cancelled due to mechanical difficulties was one that I had FIVE flats.
Now I have Slime tubes, Schwalbe tires, slime tire liners and don't get flats.
Last week, I was riding in Denver, Co. There are gobs of wonderful trails in the metro denver area. There are also some NASTY thorns there. My nephew had three flats due to thorns- then new slime tubes. I just pulled the thorns out of the tire - no leaks.
So, Jill, you can see that I could go on and on.
Oh, get a good handle bar bag. You can carry lots of stuff there. Also get rain covers for your bags. My Arkels came with the rain covers that fit nicely.