Here is what needs to be done by 3 weeks out from a big trip:
Set up your bill pay so you don’t miss any bills while away. If you will be in a different time zone you might miss a deadline and really you don’t want to be thinking about your bills while you are on vacation.
Go online or head to the post office and put a hold on your mail for the time you will be away. You don’t want to come home to an overflowing mailbox and wonder if anything was stolen or blew away in the wind. On this same note as a friend or neighbor to stop by a week and make sure nothing has been delivered by mistake and pick up any packages.
If you need foreign currency and have not yet ordered it get to your bank ASAP.
Plan for any kind of motion, sea, plan, train sickness and anything else. I just placed my order for non-drowsy Dramamine and pressure point bracelets, sickness is not going to ruin my vacation! I will also be getting a small bottle of Advil and maybe something for anti-nausea. If you have any prescriptions make sure you will have enough, if not head to the pharmacy and tell them you need an extra month because you are heading out of town.
Think about your diet, are you gluten free, vegetarian, vegan, lactose intolerant, in training? Will the food you need be readily and inexpensively available to you? If not think about bring some food bars just in case.
Is your itinerary all set and planned? If not get to planning, you are running out of time.
Do you have any pets? If so how are they being cared for while you are gone? Do you have enough food stocked up?
Do you have a plan of how you are going to contact love ones to let them know you are safe periodically? Does someone have your travel itinerary in the event of an emergency?
Trailing the blonde 
Also check your credit cards and see which would be better to use. I.e-foreign exchange fee per transaction
I always take a picture of my Passport (out of country) and/or State ID and send it to my email for reference if necessary.
Also, think about the different area you’ll be traveling and being aware of their currency and tipping nuisance.
For phone, see if your current phone is useable in other countries (may have to phone your courier) as simple as a sim (which you can buy) switch and voila.
An external charged too!
Lastly, voltage converters. We have one to lend to you for your trip extravaganza!
I have already taken care of all of the above but forgot to include it lol. Unless i put it in weeks 2 and 1. I’ll have to check hahaha
All great advice!!