I have tackle boxes, but what I find the handiest is a sturdy 5 gallon pail with the wire handle. Throw your water bottle, can of bug spray if needed, sandwich or energy bar if needed, old hat, tape, knife, bag of elastic bands, glue, small battery box big enough to hold your batteries, few tools, voltmeter, a 2' piece of stiff wire with a flag on the end (was used to mark gas line location, is now my wind sock), a small padded case for Tx. Still room for a sweater or rain jacket on top. Everything goes in the pail, place 48" wing under the armpit and plane in free hand.
Pail doubles as a table to put the wing on and by the time I get to the 3rd battery it is my chair. Very comfortable while flying and only one trip from car to the field area.
There are a lot of prettier ways to do this but haven't found anything more practical, price was right