An extremely important, but often overlooked, piece of gear everyone should have in their bug-out vehicle is a portable fuel filter, such as the Mr. Funnel portable fuel filters. Portable fuel filters remove water, dirt, and other debris from gasoline and diesel, thereby protecting the engine from harm. (They can also be used to filter kerosene, propane, and heating oil.) Clean fuel is extremely important for your vehicle (and tractor, and generator, and so forth).
Why would you need to use a portable fuel filter? At least three reasons come to mind: 1) In a bug-out situation you may be filling up using gas stored in five-gallon cans (or other storage tanks), which may have developed water issues due to condensation build-up (any air space inside the gas can will allow condensation, even if you are using additives such Sta-Bil). 2) You may be filling up at unfamiliar gas stations that you simply don't know the quality of the fuel. 3) Or, particularly in a slow collapse scenario, the quality of available gasoline may become "spotty" even with brands/stations that you are familiar with, as the infrastructure slowly deteriorates.
Portable fuel filters come in multiple sizes with different flow rates (examples: the AF1CB filter has a flow rate of up to 2.5 gallons per minute, and the larger AF15CB filter has a flow rate of up to 15 gallons per minute).
Smaller fuel filters, with slower flow rates (1 or 2 gallons per minute) are less expensive and work best for smaller quantities, such as filtering the gas going into a lawn mower or small tractor. The larger filters with higher flow rates are more expensive but work better for fueling a vehicle with a large gas tank. For example, my Nissan Pathfinder has an 18 gallon tank. A small filter with a 2.5 gallon flow rate would take more than seven minutes for a fill-up. However, a larger filter with a 15 gallon flow rate would only take a little over a minute.
Note: Don't cross contaminate. Use a separate portable fuel filter for each type of fuel. In other words, have separate filters for gasoline, diesel, heating oil, kerosene, and propane.