Comfortable shoes for walking, and not just on sidewalks, but on walking paths, and rough ground. As you go up higher in the mountains, have a jacket - for example, while short sleeves are fine in the town, you'll find it much cooler up at the top of the gondola.
Photo Equipment: Lots of film, telephoto lenses because its safer to take the pics of animals at a distance. Be like the boy scouts and be prepared! Always have a camera at the ready. That was my original tip. Today it is to make sure your camera battery is fully charged, and that you have lots of space on your memory card, or an extra one.
Luggage and bags:
Unless you like paying C$20 per day each, you can leave your backpack at home but a day pack is essential in this hiking paradise.
Clothing/Shoes/Weather Gear: Bring good sturdy hiking boots and comfy socks to handle the rocky trails of Banff. Bring synthetic clothing which is lighter per warmth factor and dries more quickly if it gets wet. Rain gear is essential and being prepared for snow at all times is a good move.
Photo Equipment: A wide angle lens is best for capturing landscapes, helping to bring the foreground into photos to make them more interesting. A good zoom is essential for capturing wildlife photos.
Camping/Beach/Outdoor Gear: If you want to stay in the park and not pay an arm and a leg, bring your tent, sleeping bags, and mats. A stove will save you heaps in eating out costs too. Campgrounds are gorgeous so take advantage of them.
Miscellaneous: A park slayer like D always comes in handy. :)
A sip up fleece is essential 1 minute warm the next fridgid. A water proof jacket & trousers that zip of to shorts are handy too
Photo Equipment: Lots - don't run out of film - there is always regret when your camera is full