Arteck 12000mAh, USB-C and 400amp dual car-starter and phone charger. This thing has a lot of seriously nice features and good reviews on Amazon. When it gets cold you want something that can not only charge your phone but start your dead car's battery.
Waterproof backpack cover. If I learned one thing about always having a backpack with things that may become ineffective they get wet is that having a waterproof cover is very important, especially in the rainy season. This one is pretty cheap, comes in at around $15 depending on your pack size, compresses into a 6"x5" packet.
Waterproof jackets - some are packable, some aren't. You can get a Columbia waterproof jacket
If you want a tactical looking waterproof jacket, check out Tactical Distributors for their Deacon waterproof jacket. This thing is pretty good looking.
Kamik Cold Weather waterproof boot. You should have a really good pair of waterproof/mudproof boots. There are a few that are hard (steel) toed boots which might work well depending on your particular situation. I have a pair of $150 boots I bought about 13 years ago which are pretty awesome. They have been worn through snow and heavy rain, through duty work and snow shoveling. These are worth their weight in gold.
Darn Tough Merino Wool Socks are the best in the industry in terms of low bulk, high quality warmth and comfort socks. The pair I have I would not give up for anything. For the fall weather the thinner merino wool socks are really a godsend, especially if your active. Standard gold toe
Flag and Anthem has some decent designs and shirts for a new company. I have one of their last years (They change from seasons to season) design long sleeve shirts and it's pretty comfortable and washes really well. They are around $50-$60 depending on type and style, they do deals, I would check them out for something non-tactical looking but still functional.
Amazon Essentials hoody. I have one of these in grey and one of their sweaters
The Dichotomy of Leadership By Willink and Babin, this is a pre-order of their hardcover (I only buy hardcover books if I can help it). If you read their Extreme Ownership book
Rite in the Rain hardcover notebook. I have several of these for duty work and they are awesome. Make sure you have a good metal pen
Vizio 28inch 2.1 TV Sound Bar, for when you are stuck inside and need to turn up the volume enough that it drowns out the rain or hurricanes outside. These new soundbars work really well.