Prudence
I am a happily child-free woman in a major urban area. I lovingly shower gifts on my nephews and friends’ children and buy their overpriced school fundraiser gift wrap. Recently, I’ve taken distance running back up after a multi-year hiatus peppered by over-partying and other self-destructive behavior. Part and parcel of this is fundraising for various great causes, which in turns gets me entry to some prestigious marathons. While I have many people in my wider network who have donated even after seeing a lone tweet of mine, these close friends say they’re going to donate but when push comes to shove, they procrastinate and/or flake out at the last minute. The final straw that inspired me to write in was that one of these friends told me yesterday over brunch that during a certain five-borough race in a few weeks she won’t be able to step a block outside her apartment for a few minutes to cheer with a sign because she has to go with her daughter to some event (that her husband could attend instead). I feel taken for granted and unsupported and hence, I’m tempted to say no the next time I get hit up for overpriced mediocre school fundraiser crap. Is it petty of me to think this way?
Edited: to add "Prudence", lest you all think this is my own angst.

Re: All of it is voluntary and all of it should be kept to one's self
Overall, I hate fundraisers and generally dont' participate. I wouldn't expect anyone to fund my entry to a race as an adult.
As to the cheering on the race thing, the lady has plans to be away from her house. Sorry not sorry. Just because you give freely doesn't mean people are able to do the same in return, nor should you expect them to.
And there always was and still is no obligation to buy school fundraising stuff, so proceed however you want there.
I think LW's feelings about the fundraising are valid and she can step back from donating if she wishes.
The cheering thing, LW just needs to get over. LW doesn't get to dictate anyone's schedule but their own.
If she's donating to the kids' schools or groups and the friends won't donate to the charity she's racing in then perhaps a discussion about why that is important to the LW is helpful.
And ditto the request to cheer. However to insinuate that friends should be asking spouses to trade places is now inappropriate. And as a parent, I'd feel pretty irritated if a friend or family member said, "You can't even step a few blocks outside with your kid to cheer me on in the NYC Marathon and instead you're going with your kid to THEIR event?" The commentary is so obtuse. Does the LW want to compare themself TO a child? The parent is attending the child's event! If the LW was constantly showing up to the soccer games and concerts of the kids perhaps there's a leg to stand on here but it's not fair to pull that line.
I used to live on the route of the Crescent City marathon. At the time, I knew a few people who ran in it. No one ever asked me to cheer them on or hold up a sign. If they had, I probably would have done it. But not if I had something else to do on that day/time. TBH, even a minor errand would take precedence over that because it doesn't sound like something that would be very important to anybody. It's one minute tops, of a friend waving hello from their porch.
And in a crowd in a pandemic with no bathrooms? I'll send you some foot rub and bubble bath.
LW, if this is the straw that breaks your over-priced wrapping paper fundraising back, that's fine. I don't think the two totally relate, but go ahead and stop participating in school fundraisers. If out of the kindness of your heart you want to give these kids gifts on birthdays and holidays go for it, but don't do anything out of obligation.