Good post... and a VERY good question!
It goes without saying that we keep an EPIRB, handheld VHF and flares on board the big boat, because we make crossings to the Bahamas, trips to the Keys and sometimes over to the Gulf of Mexico. However, I don't have all of these items onboard our runabout, as it stays inland, with an occasional high speed blast out of an inlet.
Now you've got me thinking... I probably need these items even more on the runaboat (a twin Merc 2.5 EFI, PowerPlay Sportdeck). Why? Because it's powered by Mercs! You know the old saying... "If you wanna go fast, you use a black motor. If you wanna get home, you take another color motor!"
Carl (en route to West Marine for more ditch bag components!)