Disclaimer: I've never done a solo parenting disney trip but some general thoughts from solo days out.
Don't be afraid to ask for help when you need it! When I'm solo with my stroller child, I've had so many wonderful interactions with strangers, especially grandpa-types, who will help me wrangle stroller, backpack, etc. when I need an extra hand.
Also, take your time. One night I was super stressed trying to get out of the crowded AoA food court and juggled full tray + melting down stroller child. Realized in retrospect I could have made it much easier on myself and found some free space around the food court to rearrange all the food on the tray for better stability. And it is OK to ignore the meltdown and focus on getting where you need to go next. They're safe in the stroller and one of like 3 other kids also melting down at the same time because it's been a long day and everyone is hangry! Also, we probably should have done mobile ordering more often haha
For the toilet situation - try not to wait until the last minute. If you find an empty, clean bathroom, use it because it might not be as easy later, similarly with diaper change stations.
And you probably know this but throwing it out here anyway - wear your essentials. Big backpack is for when I have my husband with me and have the luxury of time to dig through it for chilled snack containers, wipes, etc. When I'm a one person show, it's a wad of questionably clean tissues in a pocket with a squashed fruit bar.
Remember to take care of yourself! Make sure you also hydrate and eat and rest. If you're not enjoying it, it is OK to call it quits and head back to the hotel for AC and tv time.
