The resource that I use for show times is a site updated by Steve Soares. He does all of us traveling to WDW a tremendous favor by posting the current entertainment offerings. Just go to Google and type in Steve Soares. You'll then need to click on each individual park (Hollywood Studios, Epcot, Magic Kingdom and Animal Kingdom). The closer you get to your travel date, the more accurate the information will be for your particular stay as show times do change!
Once you are in WDW, pick up a Times Guide when entering each park. It will have the most up-to-date show times. However, I've always been able to plan quite accurately using the site offered by Steve Soares.
I can also provide you with a link to a PDF file that may help you start planning your March vacation. Go
here.
As for backpacks, you can and should bring one if you intend on carrying items such as water and snacks. You may bring in water and snacks. Although you pass through Security, they do not screen for food items. Alcohol, however, is not allowed in to the parks. Also glass containers are not allowed with the exception of baby food jars and perfume.
Your backpack must be no larger than 24 inches long, 15 inches wide and 18 inches high.
Have a wonderful March visit to WDW!