You've already mentioned Gitzo tripods, and I'll add the Arca-Swiss B2 head, which has the strength/weight ratio of a ballhead and the control of a pan-tilt head.
Op-Tech Hood Hats are great.
For large format, the Suunto Tandem Clinometer-Compass is a very handy gadget for squaring up any kind of floppy view camera that doesn't have levels, scales and detentes, and if you like to work by calculation (which I don't usually) measuring the angle of the plane of focus and tilt and swing angles. Yeah, I know this is the RFF, but sometimes my Technikas act like RFs and sometimes they act like view cameras.
Somewhat less expensive is an angle finding level for measuring tilt angles and making sure the groundglass and lens are plumb.
Sharpies. Always handy to have sharpies.
Gaffer's tape--you never know when you'll need it.
Little spring clamps--useful for attaching square filters to odd sized things, holding small reflectors, pinning branches out of the way, and such.
Ex-Officio shirts, which are cool in the hot weather, UV resistant, and have pockets big enough for a 4x5" Grafmatic.
Hama rubber 3-position zoom lens shade--very compact way to have the proper shade for a variety of lenses (or for zooms, but that's not an RF thing), if you use step up rings on all your lenses.
The Nikor stainless steel sheet film tank. I process sheet film in the Nikor tank, trays, and using tanks and hangers, and they're all perfectly good methods, but the Nikor tank is really a marvel of manufacturing and would cost a fortune to make today. Jobo makes something similar in plastic, but the Nikor holds 12 sheets and the Jobo only six. They still sell for upwards of $130, though they've all got to be at least 25 years old, and I recently saw one go for over $200 without the metal band that keeps the sheets in place (a rubber band will also work for this purpose, so it's not entirely useless).
Jobo sheet film clips--really expensive now at $5.50 a piece (for a film clip!), but totally worth it if you need to process a lot of film and don't have a lot of room to hang it up. The clip pierces the corner of the sheet with a pin, so contact area is minimal but strong enough for any format, and it holds the film perpendicular to the drying line, so you can hang a lot of sheets of any format in a small space. I've got 40 now.
