To your basic question, generally I start out each day as a fresh start so I wouldn't make it obvious that I was holding back a fun outing because of yesterday's disaster. But I wouldn't plan a huge day out adventure either -- mostly on the practical thought that if yesterday was bad there is a chance that today will be the same and who wants to spend mega-bucks for a day with crabby kids? I LOVE your idea of outdoor time -- that is often the best distraction/reset that I can come up with. At the end of the day, assuming it went well, I might have them reflect on why the days were different and what we could learn from that and how that should impact the rest of the summer. And if it were horrid two days in a row I would definitely sit down at the end of the day for a family meeting where I would set out some specific expectations. Same if I saw a pattern of bad days -- and in that case I might make it explicit that bad behavior one day would mean not doing a planned outing the next day. But I'd definitely give them one "pass" for the beginning.
One of my kids, even at 13, hates change and does really badly with the end of the school year into summer transition (and equally badly at the end of summer but I can't think about that yet). While this has always been the case, it has manifested itself differently over the years -- maybe that is what you are experiencing?
Since I'm a WOHM, I don't have summer days with the kids but for the years when I did I found that a loose routine helped immensely. Like Mumkinmum I had some targets for the day around cleaning up, quiet reading/summer homework time, pure veg time, outdoor play time and outings. I generally planned an outing every day, though many of those were just going to the park to play. About once a week I would do something that cost more than a couple of bucks -- a movie, an arcade/play zone/mini golf thing, a museum, the zoo... And once during the summer we would do a big day (amusement park) plus lDH always took them to the water park the day before school started. We are also blessed with the beach which I did at least once a week. We also incorporated swim lessons into the summer weeks about twice a week. Once they were past preschool age we also did at least 1 week of day camp so I wouldn't totally loose my mind.
Now that the kids are older and I'm not home, we have 1 week at the beginning of the summer and 1 at the end that is totally unscheduled for the kids. And this year they are home alone for the first time -- yikes! Anyway, during the down week they can do pretty much whatever they want as long as its cleaned up before I get home. Next week they start an 8 week round of summer day- and sleep-away camps. Less planning for me, but a whole lot more ouch for the wallet.