Along with your tent, you will want a tarp to place beneath it to protect you and the waterproof base of the tent. For basic emergency repairs, bring duct tape, a multitool, a few extra tent stakes and something to hammer them with. A rain fly protects your tent so it can protect you; ropes and a tarp strung over the tent will shield it from sun, rain, ice or snow, depending on conditions.
No matter how "hooked up" you think you are with a GPS and cell phone, it is still a good idea to bring a crank radio for weather reports. If you will be going into backcountry, bring a compass, emergency blanket, fire-starting stone or flint, and a signaling mirror.
Always carry a good basic first aid kit. Even a day-hike or overnight stay can turn bad if someone gets hurt and needs treatment. At the very least, bring wound dressing, antibiotic ointment, a general analgesic for pain, an antihistamine for allergic reactions and a small plastic bottle of water to irrigate eyes or wounds.
Body Protection from the Elements
Inside the tent, have padding and bedding appropriate to the season and conditions. Insulation is vital for cold and breathability for heat and wet weather. Basic body protection outside the tent should involve sunscreen, glasses and hats for high-sun areas (even cold mountains), breathable clothing appropriate for weather (insulated coats, hats and gloves for cold, parkas for rain, lightweight fabrics for heat). The Boy Scouts recommend quick-dry fabrics, not natural ones, because they are not flammable and can easily be dried. If bugs or toxic plants are an issue, bring bug spray or long-sleeve shirts and pants.
A clean supply of drinking water is a must. Always check to see if your campground has potable water; if not, fill a large polyethylene container with drinking water. Bring water backpacks with tube-type drinking valves, or water-treatment kits for backcountry hiking.
A hanging LED light at the crest of your tent allows good visibility, but portable lighting is also needed. Headlamps are best for tent-living when it gets dark, because they keep your hands free, a must when walking on uneven ground or moving inside the tent and sleeping bag, especially when space is limited.
Food and Waste Disposal
You will need food and, if it is not cooked, a way to prepare it. Bring a cooler to keep ice or cold food. If you will be cooking, bring something to cook the food in, such as pots and pans, and if you need a cooking stove, bring fuel for it. You will need a dishpan, soap and water if you cook food, and you will need trash bags and a way to dispose of trash and leftover food.
Safety and Regulations
You need park or land-use regulations, which can be found online or will be posted or given to you when you check into your camp. There is always good information on camping safety and ideas for storage and fire management in the pamphlets given out by state and national parks and forests.