I don't see why you'd want to sharpen bits in the field. I have a drill doctor 750 that I use for 1/4" - 1/2" bits. Anything over 3/8" or 1/2" is faster on a proper grinder once you learn the technique. I bought some of the toolroom type twist drill drawers that I have in the shop with at least 6 drills of any size that I use very often. The drills from the cabinet are used in the shop or can replace a dull drill in an index that is taken to the jobsite. Dull bits go in a plastic cup off to the side and when the cup is full I get out the Drill Doctor or bench grinder and sharpen them all and put them back into the cabinet.
The drills you buy are important too. Most drills that supply houses or hardware stores carry are carbon steel of at least HSS that aren't hardened properly. Order HSS, bright finish drills from McMaster-Carr, MSC or another tooling supplier. These will be better quality than most locally available drills and aren't all that expensive. Don't buy and Titanium Nitride or fancy colored coatings - those aren't necessary unless you're running the drill for long periods in a machine tool. I like split point 135 degree drills because they require less force when drilling by hand. The split point will break off and create a large dull spot where it was before the rest of the edge gets too dull. When this happens swap it out for another drill and it won't take too long to sharpen. If the tip of the drill is purple, brown, or straw colored it has been overheated and will take a long time to sharpen back into hard material - you have to remove at least 1/8" of length where the metal has been softened. Look at a speed and feed chart for the material you are drilling and diameter of drill to avoid overheating drills in the future. If you're dealing with employees, supply 600 RPM Hole Shooters to minimize the drill bit speed.