I was confused about this myself, as I had a dive package which included breakfast. I wasn't sure whether I should tip at the end of our stay or after each event. It turned out to be quite confusing since I waited until the end then tried to figure out who served me at which meal and which DM I had for each dive. I finally asked the waiter and he (gratefully) explained that it was far better to tip at the end of each meal and each dive since chances are that you won't have the same server/ dm/ maid each day. He also said that a majority of vacationers tip at the end and then they (the staff) end up getting short changed. He said this was especially important during the slow season when they don't make as much money anyway. I wish I had known this beforehand. I went to the bar for a cold drink or a quick snack after each dive and never had money with me since I was in a hurry to get back on the boat for the 2nd dive. I put everything on my room tab but when I was ready to tip at the end of our stay, couldn't figure out how much to give each person. The waiter also stressed that it was better to tip in cash and not add it to the credit card since they don't receive the tips for weeks, if at all. Hope this helps!
As for amounts:
Each dive: $10 US or $20 Belize for the DM. I gave the assistant approximately $5 US per dive, but I used all my own equipment and set it up myself each time, including analyzing and switching out tanks. The assistant just helped me out of the water. If you use the resort's equipment and they set your gear up for you then tip more.
Meals: 15-25%
Baggage: $5 US per bag/ $10 Belize
I tipped the tank filler a little extra for my Nitrox tanks but still analyzed and carried them myself to the boat.