Just as your runner will spend time assembling items for the race, a well-prepared Ultra Crew has its own gear to go with a well-thought out support strategy. Some runners are very specific about what they want to have on hand and when. Others will feel most confident having everything in drop bags and won't have planned requests at every aid station. Talk to your runner in advance about their expectations and how you can best support them. Whatever the approach, one way to be useful to your runner is to be organized with stuff you need yourself. Ideally, you're packing light.

First aid kit: Be ready to address minor injuries - have bandages, gauze, antiseptic cream, pain relievers handy, preferably brands they trained with.
Backup Hydration: The runner will need to stay hydrated throughout the race, so make sure there are plenty of water bottles and hydration packs available.
Energy gels and bars: These are great sources of quick energy and are easy to eat on the go. Make sure to pack a variety of flavors to keep the runner from getting bored.
Sunscreen: Even if the weather is cloudy, the runner will still be exposed to the sun for hours on end. Sunscreen will help prevent sunburn and protect their skin from damage.
Insect repellent: Depending on the location of the race, the runner may encounter mosquitoes, ticks, and other insects. Insect repellent will help keep them comfortable and protect them from insect-borne diseases.
Headlamp and spare batteries: The race may continue into the night, and a headlamp will be necessary for the runner to see the trail. Make sure to pack spare batteries, too.
Warm clothing: Even if the race starts out warm, the temperature may drop significantly as the night wears on. Pack warm clothing like a jacket, hat, and gloves to keep the runner comfortable.
Anti-chafing cream: Long-distance running can cause chafing, which can be painful and slow the runner down. Anti-chafing cream will help prevent this.
Blister pads: The runner is likely to develop blisters during the race, so pack some blister pads to help keep them comfortable.
Snacks and comfort food: Running for 100 miles is a huge physical and mental challenge, so the runner may need some comfort food to boost their spirits. Pack some of their favorite snacks to help keep them motivated.
Maps and directions: Make sure the support crew has detailed maps and directions to each aid station along the race course.
Cash and credit cards: The support crew may need to buy food, drinks, or other supplies along the way, so make sure they have cash and credit cards on hand.
Mobile phone and charger: The support crew should have a mobile phone and charger to stay in touch with each other and with the runner, and to call for help if necessary.
Folding chairs: The support crew will be waiting at each aid station for several hours, so folding chairs will make their wait more comfortable.
Camera: Capture the memories of the race with photos and videos of the runner's journey.

Chair or Hammock: You are potentially going to spend some time waiting for your runner. You may as well do so in style and comfort. Key here is being able to relax a little but also not be in the way of every other person who is trying to relax and watch for their runner.

Color Cloud Hammocks were featured on the Side Hustle School podcast. The company features eye-catching designs, comfy styling, and a socially conscious business model.

A Crazy Creek Chair is also great for being portable, comfortable, and convenient.

Blanket or Sleeping Bag: It gets cold outside at night. Bring something to keep you warm. The Ultra Crew is currently fascinated by this item from Poler, because a wearable sleeping bag seems like an idea whose time has come.
Layers/gear for rain, cold, sun, or other potential weather conditions (for you): Consider the weather conditions and plan accordingly. Items to consider: hat, gloves, rain jacket, warm jacket, warm socks.
Headlamp (for you) + extra batteries (bonus points if you bring extra batteries for your runner too). Here are a few to consider:

Entertainment/Motivation (for you): In no particular order, below are ideas for books by Mirna Valerio, Dean Karnazes, Hal Koerner, Kilian Jornet, and Scott Jurek.

Something waterproof-ish for documents like:
- Emergency contact info for your runner
- Phone numbers of other crew members
- Driving directions to aid stations
- Runner guide for the race
- Pacing information for your runner - what time you think they'll be at each aid or crew station
- If your runner sent you an email or gave you a list of things to remember or to do, by all means, bring that.

Important Reminder: If you don't want to print these things, make sure they are accessible without a cell or wifi signal

Good understanding of the course proceeding from the current aid station
Duct tape
First aid kit. One item that recently came in handy was Benadryl or some other anti-histamine, because you never know when your runner will get stung by a swarm of hornets.
Something to put it all in: While the perfect crew bag may not have been invented yet, there are good options out there for storing your stuff and your runner's stuff in a way that's organized, efficient, and useful. Key features include the ability to carry the bag different ways (like using optional back pack straps) as you may have to hike to an aid station, and features like compartments and waterproofing.

Here are two "specialized" crew bags:

You could also repurpose another bag - look for something that's durable, easily carried, and, ideally, waterproof or water resistant.

Patagonia Black Hole Duffle. If you look at reviews of this bag, you'll find people commenting on how they can always squeeze just one more thing in. They aren't kidding. What's more, the zipper is tenacious, the construction is durable, and it only took one online video to understand how to get the removable backpack straps to attach.
North Face Duffle
Poler High & Dry Roll Top

Don't ignore the timeless utility of resealable plastic bags for items you want to keep separate (we're looking at you, socks that got jettisoned at mile 60) and organized (like energy bars, batteries, etc.). The extra large ones that you can basically use like a compression bag come in especially handy for stowing a change of clothes.

A way for your runner to spot you easily: An Inflatable T-Rex costume just doesn't get old.

Spotted at the Leadville 100 Twin Lakes aid station