A few ideas off the top of my head:
Fishing kit box with a flat kite string winder as the reel that fits in the box, already rigged.
Game cart flex/swivel hitch unit and belt to attach to various game cart handles so they can be pulled hands free.
Anti-tangle bank line dispenser (also 550/750 cord dispensers)
Stand up tent stake driver & puller for those of us that can't bend down or get down on our knees and then back up very well. Might be designed to also be used as a tarp tent support pole. Perhaps with a line of stakes similar to the MSR Groundhog line of stake designed to work with the driver/puller. (If you want details on the design I have in mind, PM me.)
A modern materials, fold up, atlatl with folding dart similar to the ones you already have.
A bellows/pump/tank assembly to use with quality, large caliber blow guns for those of us that can't get a deep enough breath to make effective use of blowguns.
A lightweight, fold up latrine support frame to make using a trench/pit latrine easier for those of us that can't squat down and get up un-assisted.
A much better design credit card tool
An EDC carry slim line elevator door opening pry bar
An EDC very flat, clandestine restraint escape micro tool with handcuff key, cuff shim, seat belt cutter type cutter for tape and zip-tie cuffs. Must be very flat so it can be carried in a slot in the pants waist band, etc.
A long, folding, shock corded, twist lock multi-use pole with long lanyard. With fish/frog gig head, fish spear point, recovery hook, rubber tip, ice tip, etc.
A converter/direction changer antenna coupler to allow use of a Yaesu FT-897D Amateur radio with attached auto antenna tuner as a back pack radio with the antenna coming up vertically out of the pack, so it can use standard antennas, including a 108" SS whip, with UHF, BNC, and whip thread adapters.
Quick on/off no-rubber, shoe ice spikes
A pair of quality, tethered, compact, protected push through, ice escape picks.
A quality, leak proof, single fill, Zippo lighter fluid tube. Better leak proof design (double/triple O-ring seals) than the Zippo model
An improved, lighter version of the German GI nesting knife/fork/spoon, can opener utensil set
Lightweight stainless steel 'sandwich box' size latching storage boxes (rectangular/square)
An Esbit solid fuel type folding stove tall enough to use the Esbit alcohol burner
A wilderness rolling pack carrier using wheels and designs similar to the Cabela's Super magnum dual wheel game cart or the Dixon roller pack, slimmer than a game cart, but wider than the Dixon, and designed to use a waist belt and carry several packs/duffles/etc.
Just my opinion.