Reddit mentions of Spenco 2nd Skin Blister Kit Sports, 24 Count

Heck Yeah!

ProTip: If you are going to wear them a lot then make sure you:

1. Break them in by wearing them some this week.
   
   
2. Pack a blister kit.

Hi! I don't know what your experience level with running or hiking in general is, so I apologize if I give any advice that you already know or seems obvious.

I've used a knee sleeve before, and found that (although it was helpful for short periods) it got pretty uncomfortable after a few hours. If you do use one, make sure you're able to quickly take it off. On a similar note, if you have compression socks, I know people who really like wearing them on long hikes, but that's anecdotal and may not work for you.

Seconding the advice about non-cotton clothing and extra socks. I'd get a couple hand/foot/body warmers just in case, depending on how warm the rain is where you are. Keep your core temperature up. Wear a rainjacket or at least a poncho. If you've got a backpack that's not waterproof and doesn't have a rain cover, you can put a thick trash bag inside to keep your gear dry.

If you have a foot roller, lacrosse ball, golf ball, etc., I'd suggest bringing that along. You can roll your (bare/socked) foot on top of it as a quick massage. Be aware that your feet will likely swell up to at least some degree. This is more of a just-in-case type of thing. (Speaking of feet swelling up—when you take breaks, elevate your feet for a few minutes.)

If the course is staffed with aid stations, they'll likely have first aid supplies for blisters. If not, or if aid stations are far apart, see if you can get ahold of 2nd skin or something similar (this or this).

Carry some food, even if you don't end up eating it all. I like making trail mix with nuts, dried fruit (dates/cranberries), and dark chocolate (M&Ms are nice b/c they don't melt as badly, though 'dark chocolate' M&Ms are…not really dark chocolate).

Leave a towel and dry clothes in your car/with friends/in a gear drop bag if any of those options are available. Being able to change into fresh, dry clothing is wonderful.

Don't carry too much stuff. Walking 35k gets much harder as you add on extra weight, especially if you're worried about your knees. Water is important, though, so don't skimp. You could also fill a bottle up with sports drink/Tailwind/Nuun. (If there's a lot of aid stations, such that you won't be going longer than 30-40 minutes between, you might not need to carry a ton of water, but it's still good to have some).

As for preventing boredom…depends on the course, but I get surprisingly not bored on long hikes, especially with a friend! Since you're doing this for charity, I'll mention that I know some people dedicate certain sections (each mile, every few km, etc.) of their run to particular people or causes in their life. That gives you something to think about and keeps you going through the hard bits.

Be safe, and have fun!