Do any of you use an app or something similar to mark spots down you want to visit, eat at, drink at, explore etc while on a trip?

I use Instagram. I follow various restaurants, tour companies, etc, and save things that look interesting.

Following. My wife and I have a shared bucket list trip iPhone note. We use it to list where we want to go and ideas for each place as we come across them. But I've been starting to replace our shared notes with designated apps as they typically have better features.....

Google Trips

Trip Advisor. They also have a Travel Timeline fiction that tracks everywhere you go and then maps it. Playing with it while in Iceland right now.

I use Trip Advisor as well to tag some sites to visit while I'm in the planning stage.

I really like AllTrails to find good hiking trails with reviews. Used that a ton recently.

Once I have the sites down, I just use Excel & make a spreadsheet of day to day activities and carry around a hard copy like the old man I am. I usually limit the activities to 2-3 "big" things to do in a day. There is a grab bag of smaller activities I'll put off in another column that we'll do if we feel like it or have time.

By the way, the Travel Timeline feature on TripAdvisor stopped working and was a bust. Google Maps has the exact same feature and works very well but that's probably because they are evil tracking capabilities are top notch.