well, it depends on several things per my experience.
you'll only need 2 changes of clothes for 3 days.
what you'll be wearing when you leave out will take care of the first day.
if you bought a new Harley, then you are automatically enrolled in the HOG group, so you'll have $100 for road side assistance....(I know
how far will you be during your trip from any civilization?
will your cell phone work all along the trip?
are yall sleeping in tents or at a hotel or the like?
anytime, especially this time of year in the heat, always take a few bottles of water at least, even warm water is better than no water.
if you are subject to cramps in the heat, then take what are called pickle pops, they don't have to be frozen, (walmart or most sporting goods), or straight dill pickle juice, will get rid of cramps with in a couple of minutes, trust me, I know!
how many miles between fuel stops?...some of these bikes get freaky after 90-100 miles on a tank of fuel and will not go much farther.
rain?....I'd at least take a rain jacket. ...if it gets raining too hard, then stop where you "safely" can and wait it out, normally the heavy stuff will pass shortly. ...and not under an underpass or on the shoulder of the road, other drives may not see you and things could get real bad real fast.
take all the meds you'll need, if you need to.
even a small amount of tools can get a out of a jam, I try to take multi-use tools where I can.
tank bags are great and allow you to get everything out of all your pockets, ...i...e..keys, wallet, glasses, phones...etc..
don't wear real loose clothing, a flapping collar gets irritating quick.
never assume everyone will give ya the right of way, watch intersection closely! always pay attention to whats behind you. especially if you are not in a familiar area.
never drink alcohol any where near driving a bike.
watch the speed limits, especially small towns, they make their paychecks off of the unsuspecting or inattentive travelers.
if you got anything strapped on your bikes, then be sure it is all secure!
always let some one know, when you are leaving, when you expect to get where you are going, the path traveled if possible, when you've arrived and all this on your way back, it's just the responsible thing to do now days, and it can save a lot of anguish for you and others!
I'm sure there is more others can come up with, but this is my 2 cents.
most of all, be safe, don't rush, pay attention and enjoy the trip.