Hood struts
with a lifetime warranty, and grilles, rubber cargo mats, floor mats, etc... non-OEM upgrade parts sort of like what JCWhitney has done for years... though this is also an established market. Transistor, bolt(s)/nuts/lock washers +heatsink grease (as a kit) to repair blown EATC (automatic climate control) blower motor speed control module (this is not a stock part, would be a you bundle it repair kit), and blower motor resistor module for vehicles equipped with manual climate control.
High flex (high strand count) 14 or 16 gauge wire in ~ 2' lengths for driver's door (hinge area/boot) wiring repair. It would be better still as a kit that includes 1 ft. of 3/16" (or 1/4" if it has thick insulation) heatshrink tubing, and ideally wire colors in somewhat matching color options to the OEM wire but that might be hard to source.
Touch-up paint in all the gen II OEM colors. Motorcraft has a nice combo bottle for some Ford vehicles that includes both the base color coat and clear coat in the same double-well bottle... not sure if they package it like that for gen II Explorers.
LED replacement dash, steering wheel, and other aux. lighting bulb replacements. Bolt-on/ready-to-install LED upper brake light upgrade/replacement on early gen II models.
Body plugs for holes left when running boards are removed, or a finishing trim strip to cover them. Aftermarket stereo adapter plug/pigtail (wires) for the few different OEM stereo configurations, and adapter/cover plates for aftermarket stereos... maybe throw in a radio removal tool if it's cheap enough to do so.
Window motor gear repair kit, improved thermostat housing, metal radiator fan blades... basically, just look through the topics on this forum to see what the frequent failure parts are.
If you really want to be radical, develop customizations that nobody else offers like a 3' x 6' polycarbonate sheet moon roof and gasket set (some vehicle cutting required).
or maybe a rooftop mounted, encased solar panel battery maintainer with all hardware and wiring (ready to bolt on)