Tomorrow I'm towing my boat from Lake Anna to OBX, about 250 miles. Just trying to make sure I don't forget anything.

spare trailer tire
tire pressure gauge
grease gun
car ramps
wheel blocks
heavy duty jack
tools
transom tie downs

What else am I forgeting?

Boat

Spare trailer wheel bearings greesed and ready to go.
I also like to carry a BIG ratchet strap in case you do lose a wheel bearing you can tie an up that wheel and limp it off the highway.
Been there, done that

4-way Lug Wrench

ROFLOL!!!

I also tie down the front with a ratchet strap in addition to the bow strap on the trailer. Keeps the bow from bouncing.

A spare set of wheel bearings, races and seals. And the tools to change them. After a failure a couple years ago I always carry them.

What are the car ramps for?

I always carry some extra replacement lights too. The replacements are cheap, and well worth having if you need them.

I did a search on how to change a flat tire on a trailer w/ torsion springs. One method was to drive the non-flat axle up on the ramp susepnding the axle with the flat tire in midair, thus making it easier than jacking everything up.

Makes sense. A 4x4 block of wood will do as well. It also comes in handy for chocks and a prop block.