I have Mondays off of work so Mondays are my appointment days. It helps me to have it be consistently on the same day. So Sunday night I just have to check the calendars. Speaking of calendars, I use both my computer calendar and my phone calendar.
In the beginning, I had a chart created on word that had the time, med, dosage, blank spaces, and a key including how to make the formula with added cals. Now, I just know. After 8 months of being home, I have it down to a science.
I have a file folder where I keep all of his med info. I bring it with me when I go to a specialist.. But I am a freak and actually know everything in my head sooooo I rarely refer to the folder.
After I see a specialist, I call my pedi on the way home to update them. She has been great about communicating with the doctors too.
I agree with pp about bringing extra food, I also bring a few toys... You can wait for a long time!

As a twin momma...bring help whenever you can (although I admit sometimes its better for my sanity believe it or not, to go at it alone because I am just so used to doing it my way). I know what offices are helpful when it comes to having both babies in tow (our Ped and Eye Doc's office is fabulous, our Ped's nurse will walk out to the car to help me carry a baby in and so will the Eye Doc). Now that RSV season has hit in full force I try whenever I can to get a sitter for one baby if he/she isn't the one being seen that day. (This doesn't work out often, but it is great when it does.)
Always have extra bottles/food and/or feeding supplies (or for doctor's visits I bring 1 bottle per baby and will grab a bottle of the ready to go formula from the store to take instead of multiple bottles) because you never know how long you might be waiting.
When they were on medicine's I kept an updated list in the diaper bag to take with me, I also carry a small plastic file folder ($1 section at Target) with their most recent visit summaries in it so that if one doc doesn't have a copy of our most recent visit with another doc I can provide him with one. I haven't had any MAJOR issues yet with doctor's communicating together, the only time the Ped might not have updated info is if we see the Ped within a day or two of our last specialist visit.
And my biggest life saver of all is a good day planner, I am a visual person so it helps to see what we've got going on that week. I've got one of the ones with tabs for each month- a month at a glance & then pages for daily planning. Where the pages for daily planning are I jot down the appt info as well as the address/location and phone number for that visit so I have it at my finger tips. I've also tapes the cards for all the doctors to the inside cover of the book so they are right there as well.
I confess, I probably wouldn't be this obsessive and organized if they weren't preemies with lists of doctors, meds, etc.

In an age were it can seem easy to keep track of all doctor visits and other records on a cellphone calendar or find an app to joint notes, I find that traditional paper and pen method is best. I carry a small pocket size calendar were I can get a tangible look at our schedule. I also have a thin business card holder that I can easily insert into the fold of the calendar. Whenever I visit a doctor or clinic I grab a card and stick it in the insert. This way, if I need to call to make or cancel an appointment it's all in one spot. I also carry Isabella's immunization card in the there. I have several copies if our discharge papers that I give to all our doctors. This way, when were done with an appointment I ask if they can please mail a report to the pediatrician listed on our discharge papers. So when we go see our Pedi, he has all the reports and we can discuss "were to go from here".

Also.... I always ask that I be contacted by cellphone, since I always have my phone around. Before, I had listed my home number as the primary number and if I got called when I wasn't home (usually when office is closed) I would sometimes forget to call back.

Our baby has a "calendar" I carry around with me - we note everything in there, her meds/dosages are in the "notes" section, I note every time there is a change, I also carry copies of discharge papers and when we see any specialists we ask for a copy of their narrative report, I provide all the copies myself to her pediatrician. We also have a wall calendar in the Kitchen - I add all her appointments on there as well because we use it with her Nanny - We also use the kitchen calendar to note which one of us (DH or I) are taking the baby to the appointment and when we are working/off work etc. We have a medication/feeding schedule on the fridge and I have an app on my Ipad where I track baby's weight, height (it plots her growth chart) etc.