Stuff to take on Field Day

These are essential items I take on field day. 

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Wireties. You will use them by the dozens. I like to put them on the end of U-Bolts to keep the nuts from vibrating off while I am driving.  I prefer the flourescent ties from Harbor Freight.
PVC Tape.  You will use a lot of it.
Velcro ties. These are commonly used for computer cables, but they work well for securing any sort of wire and cable.  http://www.lowes.com/pd_172729-388-90924_0__?productId=3017542
Jumper cable bags. Bucket Boss makes nice canvas bags that are ideal for carrying coaxial cable.  http://www.amazon.com/Bucket-Boss-06009-Jumper-Cable/dp/B000022688
An electric screwdriver will save you a lot of time.  Be sure to bring spare bits and the socket wrench ends.
A good work table is a must. I prefer a pair of collapsible plastic sawhorses with a piece of plywood on top. The sawhorses are also handy to rest antennas on during assembly.
A stepladder is very handy. I prefer the "Little Giant" type that can be extended and also used as a regular ladder.
PL-259 and SO-239 caps. They keep those nasty little bees from plugging your connections with mud and help keep the connectors dry.
Coax adapters are a must.  You can't have too many barrels or elbows.  I carry mine in a compartmented case.
Rubber faced gloves.  I prefer the Atlas Therma-Fit.  They give you a good grip on things and are surprisingly warm.
Signs.  It amazes me how much respect people pay to signs.  This is one of my favorites.  I have several "Emergency Communications Exercise" signs that I display prominently - this explains the cables and antennas and saves answering a lot of questions.
Rope.  You can't have too much.  I like to rope off my operating area.
Surveyors tape.  Some people call it flagging tape.  It is handy to mark cables on the ground or in the air and will keep somebody from driving into your cable or clotheslining themselves on it.
A fire extinguisher.  I like the compressed air models that squirt water.  If you are camping on public land put it out in plain sight with a shovel.  Visitors from the Forest Service and the Park Service will notice them, believe me.
Tubular foam pipe insulation.  If you are in a RV or operating mobile it is very handy - slide the split side over a window to seal the gap when you run cables out the window.    http://www.lowes.com/Pipe-Fittings/Pipe-Insulation/Tubular-Pipe-Insulation/_/N-1z0zq5s/pl#!