Luggage and bags: Any type of luggage is fine but, a backpack is great.
Clothing/Shoes/Weather Gear: I would recommend coming prepaired for any kind of weather. You never know when it is going to drop below 30 degrees F. It could be 80 in Ashford and only 50 in Paradise. Dress in layers - Be prepaired!
Luggage and bags: If you're backpacking and hiking pack light. But include the items listed below. Buy your food prior to reaching the site. The cost of consumables increases rather dramatically the closer you get to the park.
Clothing/Shoes/Weather Gear: If you're visiting during the winter months bring good hiking shoes or snow boots with excellent tread. Warm clothes are a must and if your camping make sure you have sufficient blankets to keep you warm. Shorts are recommended for summer time and at least two pairs of pants because the night air in the mountains is a lot cooler. Make sure you bring a gortex or rain coat of some sort. Gortex's usually come with a liner so you can use it as a warm coat as well.
Toiletries and Medical Supplies: Always bring a first aid kit. If your camping there isn't any medical facility readily available for you. Bring sun screen for summer.
Photo Equipment: Most of the pictures I have posted were taken with a 'plain jane' 35mm. You don't have to be an expert or have fancy equipment to get awesome pictures here.
Camping/Beach/Outdoor Gear: Camping: sleeping bags are a must! Extra warm bedding is recommended even in summer and some camp sites are really rocky, so if you need a little more comfort invest in an air bed. Get firewood, before you get here if you can, if not, wood and kindling can be purchased at each campsite for approximately $10 US for a bundle of wood and $5 for kindling.
Miscellaneous: Just a tip: If you plan to visit the park more than once, or if you have more than one park to visit purchase the Parks annual pass. It's $25 US and it will cover all access fees for all of Washington's Parks. This pass is per car not per person. If you have more than one vehicle you will need to buy a pass per vehicle.