Depends on the total length of the run, which means distance to and back (round trip). I would guess at least 10 AWG, but see the chart below and assess what your worst case total amp load would be.
An example (using the 3% max voltage drop chart), say a 16 to 18' total run, where you need to carry 20 amps ON at any one time ... that means you read the green colored band to determine the wire size needed, which is 10 AWG.
14 AWG may be overkill for most of those circuits to the items, less maybe the bilge pump. LEDs are well < 1-amp each, usually in the milliamps. Small pumps 3-5 amps, mostly due to starting voltage, and fishfinders are 1-2 amps. I've used 16 AWG for most load items and 18 AWG or smaller for LEDs and other ultra-low voltage items and have never had an issue. The only time I'll do a calculation for stuff like that is high draw or safety items, e.g., bilge/storm pumps, or that accessory 12V socket that you never know what someone may stick in it.
Your items spec sheets or manuals list the amp draw. And if you use something like a spotlight measured in watts, just divide the wattage (say 55 watts for a 12V spotlight) by the DC voltage, to get the amps. Example: 55 watts / 12.6 (nominal VDC) = 4.4 amps.