A friend of mine is plotting a long work trip where they will be hopping from city to city for about a month. They know that I have done work travel like that and asked my advice.
On that kind of long work sojourn, the temptation is to travel Well Prepared because you are going to be On The Road For A While. But I recommend traveling as light as one can. This kind of trip in particular means packing and unpacking a lot, maneuvering through airports, loading in and out of cars. You don't want to bring more than you can carry for a distance ... because at some point you will have to.
I keep my travel kit packed all the time, and bring the same stuff whether on an overnight or hitting the road for a month, whether staying somewhere for a long stretch or roving around. That makes me ready to stay on the road indefinitely, because on a few occasions I have had to extend my trip by a day or three ... or a week ... and I want to always stand ready for that.
One of these days I will have to write about my whole travel kit in detail. For now, an overview relevant to this type of travel, with links to products I recommend.
I have a sub-maximum carry-on for the overhead plus a comfort bag for under the seat in front of me on the plane. I actually own two different carry-on options — a rolling pullman case for work travel and a backpack-able soft case for most personal travel — but I pack the same stuff either way. I have a bunch of recommendations for makers of these.
The comfort bag contains everything I need to have available for my animal needs on a plane or elsewhere, plus my laptop, tablet, and Kindle. I always keep it close enough to grab, and it fits on my lap if necessary. It has my neck pillow, blindfold, dorky mouth-and-nose mask, noise cancelling headphones — water bottle and electrolytes — convenient-format caffeine, melatonin, drugs, spices, and wipes — a plain white shemagh — and all my cables, batteries, and power converters. With a mini extension cord which turns one plug into two outlets, I can ask someone to let me cut in if they have taken the only available power outlet somewhere. Plus I leave a little room to tuck in some snacks: manage that blood sugar!
The carry-on has my clothes and other stuff that I only unpack on arrival. At this point my entire travel wardrobe is made of technical fabrics or merino wool that hold up to a beating and wash & dry easily. That makes it easier to travel with a small wardrobe with confidence.
(Update: a friend was surprised that I did not mention my enthusiasm for packing cubes. Packing cubes are a godsend. They make it easy to pack tight without your bag exploding when you open it. I usually take the cubes out of the bag and just lay them in the hotel dresser, still packed. I am particularly fond of cubes with a mesh side, compression zippers for squeezing the contents tight, and two-chamber cubes that pack clean and dirty clothes into the same tidy space; it seems that one can find cubes which do any two out of three, but not all three. Eagle Creek make an array of well-constructed options.)
In theory one can do ultralight travel and get it down to One To Wash And One To Wear but that means never ever skipping a day from being too tired or whatever. Better to have a buffer, but not too much because that means traveling with more kit and facing the dangerous temptation to not Always Be Laundering. Handwashing laundry in a hotel room it is hard to do more than two changes at once, so one can easily end up with a dirty laundry deficit that is hard to pay off. I pack four days of clothes and wear one, which gets me through a normal work week. But my kit always contains a clothesline, washbag, and soap. One can just do laundry in a hotel sink but having a Scrubba bag helps a lot. The instructions show a person agitating the bag with their hands but it is a million times easier to set it in the shower and stomp it for a few minutes with your feet.
One travel garment I strongly recommend is a middleweight zipper cardigan that zips all the way open or all the way up into a turtleneck-like arrangement. You can wear that under your jacket and be warm enough in pretty cold weather and it is easy to regulate temperature with the zipper. If real cold weather is a possibility, a light hooded puffer jacket layers nicely and covers a lot of situations while packing small. And whatever the weather I always pack a light rain jacket / windbreaker.
Aside from kit, you have to get your head right. When doing this kind of travel it is very easy to succumb to FOMO. “I have this one chance tonight to see a little of Chicago!” But on the long sojourn, the enemy is Creeping Exhaustion. Your first priority must always be taking every opportunity for rest you can get. It is 100% legit to hide in a hotel room or a host’s guest room. You will see and do more in the long run if you jealously guard your energies.
Getting to sleep in a strange bed, fighting jet lag, can be tough. I knock myself out with a cocktail of Benadryl and sublingual melatonin; melatonin forces the body clock but I find that if I don't fall asleep when it first makes me drowsy I end up with insomnia, so the Benadryl forces me to zonk out enough that the melatonin can take hold.
And never forget the ABC of travel: always be charging.