Diaper selection aside (Seni Super Plus are my day wear)
Diaper covers! For the day I use pull on plastic pants, this is mostly to prevent leaking due to press-out if I'm not able to change when I need to.
Onesies! I wear a tshirt styled onesie to work. Looks like a tshirt, keeps the padding hidden. The cheep chinese ones that were mentioned earlier work great. I got one initially, and have bought several since.
Diaper Bag! messenger bags and backpacks work great. I keep a couple diapers, wipes, a small waterproof laundry bag, and sunscreen in mine. You could of course add powder, creams, lotions etc. When I am at work I prefer the bare minimums.
Couple other bits of advice, start thicker. When I started with Seni I wasn't sure what to expect so I started with the Quatro just for a bit of ease of mind. Once I figured out that they were a bit much for my needs I stepped down to the Super Plus.
Find a brand you like that fits your budget.
For me I can typically get through work without changing. I have also learned to judge capacity by the feel. Once I reach a certain point, I know I am going to press-out if I wet anymore, so I go change.
Messing is a whole different consideration. I don't like to be messy at work. If I am at the shop or at a clients site, I will use the restroom. If I am on the road, I will change in the back of my work van or at a rest area. It is very rare for me to mess during work hours. If you do need to use the restroom don't forget the long onesie snap, it will fall in the toilet.
Either way, it is a good idea to figure out your typical routine so you can plan your changes. When I was still in an office, I would change during lunch just to be safe. Hope it helps!