So a lot of these things can be remedied by writing them down and keeping your lists with you. I like to keep sticky notes in multiple rooms in my house and in my car and I always have a pen on me so I can write things down as soon as they pop in my head and I can put the sticky note on the cover or inside a notebook that I carry around.
Make a checklist for the day on a sticky note and put it on your bag. Start writing the checklist a day ahead and throughout the day or if it’s mostly the same list every day get custom stickies made with your base list on it and room for extra things. DO THIS FOR GROCERY LIST ALSO.
Fill your water bottle before going to the toilet. Think of the toilet as your reward for filling the bottle. You probably won’t forget to pee between classes.
As for the timer, for me I need to visually see and interact with the time passing to help me not be distracted. I love using hourglass timers for that because they catch me visually when my mind starts to wander and remind me to stay on task and see how much longer I have left. I’m interested in trying a Time Timer as well …we shall see if Santa thinks I was good this year for that.
An expensive suggestion for the calendar thing is something along the lines of an Apple Watch. I love mine bc I tell Siri to put it in my calendar right away. I also use it to set timers and alarms. I can set reminders like “turn off coffee maker” too 🙂
Other things that may help in addition: getting a full and restful night of sleep, drinking enough water, eating enough protein, reducing intake of toxins in foods/skincare/etc (which can cause inflammation in blood-brain barrier), eating foods that support cognitive function, avoiding added sugars and simple carbs, getting more movement into your day even if you’re already active, avoiding marijuana (sorry but the benefits are likely not going to outweigh the issues if you’ve got severe brain fog) and alcohol, getting enough positive social interaction (can increase dopamine!).
Also, stimulant medication if you’re not on it.