Sink cabinet and counter

If building from scratch, the shortest straightest dryer vent possible.

Table or countertop for folding clothes as the come out of the dryer.

Plus a spot to hang an ironing board and iron, and enough floor room to use it. A shelf for laundry soap, softener etc. and room to store 2 laundry baskets side by side. Storage for broom and mop and possibly a vacuum cleaner. Storage for miscellaneous items would be fantastic, paper towel, vases for flowers, extra towels and linens. Enough counter top that there is clear space to actually fold clothes. Bright colours and a piece of humorous art.

A washtub/sink to hand wash delicate items, some room for hanging items that can't go through the dryer so they can drip dry, also a flat area where items like sweaters that have to be laid flat to dry can dry. A floor drain with appropriate drainage just in case a hose breaks or the washer leaks - easy to do in a basement, but on upper levels this can be done with a catch tray under the machine and a drain. I agree with Orangecamera about the shortest & straightest dryer vent possible. I also want a trash can for the lint I clean out of my dryer screen, and the used dryer sheets or other trash I remove from pockets before washing. Also, the dryer vent should have an appropriate cover on the exterior of the house to prevent critters from entering it - or birds from building nests in it.

Good lighting, trash can, closet rod for hanging things. Shelf for detergent.

Valuable input, thanks everyone! Will need to consider especially sink, since we didn't plan for one. The rest I think we can accomodate.

Does anyone have an opinion on placement of dryer and washing machine? Is it best next to each other or is on top of each other ok too? The latter would save some storage space I think.

Here are two articles on making the most out of a laundry room.

https://www.houzz.com/magazine/get-more-from-a-multipurpose-laundry-room-stsetivw-vs~13176360

https://www.houzz.com/magazine/7-day-plan-get-a-spotless-beautifully-organized-laundry-room-stsetivw-vs~25919468

Stacking your washer/dryer can be done if they are front loaders. There are some combo stacked units that are top loaders but I have not been impressed by the ones I've used. The trick with stacked units is making absolutely certain everything is properly leveled so the machines don't vibrate or try to "walk" off each other if the load gets off balance. Additionally to consider is the height of the individual doing the laundry - some shorter individuals like my grandmother would find it difficult to reach into the upper machine.

Personally, I prefer my front loaders side-by-side with the doors opening in opposite directions, sort of like those fridges with the french doors, so that when you switch a load from the washer to dryer you don't have to dodge a door. I prefer to have my front loading machines on the matching pedestals so that the height is easy to lean in without bothering my back.

You haven't asked, but if you are designing your laundry room from scratch, I'd be sure to have it set up so the dryer can be either natural gas or electric so that if you have to buy a new one in the distant future you can get whichever type will be the best financially. I personally prefer a natural gas dryer.