back to the original basics of the question:
there are plenty of $40 options that are there for the high end of the market.
The $10 ones are lacking.
Go for $20-25, stainless, no aluminum, sharpenable or replaceable blade.
Maybe a plastic handle? Floating or lanyard? Must cut up to 1/2"/13mm line.
On to bells and whistles:
Wear the whistle around your neck.
Possibly on a piece of 3/4 to 1" webbing that can also become a tourniquet -hopefully not for your neck, it should have a releaseable buckle!
Or carry an extra kite leash or paracord, many uses including tourniquet, tow rope, landing tether etc.
Maybe your knife can be used to secure/tighten tourniquet.
It could also be used to shred your clothes or kite to make a tourniquet, bandage, splint, etc.
I don't have a vhf radio though I sometimes ride alone -but within 5-10 miles of a USCG station. Floating handheld vhf is about $150-200.
I'm cheap and don't like feeling encumbered, but I'd feel pretty dumb if I ever needed them.
Probably a good idea to be more of a safety guy. I'll try to remember my helmet at least.