Map & Compass
You should always carry a map and compass even if you use GPS navigation. You should also learn how they work in conjunction with one another. There is useful information on the Ordnance Survey site, with links to a map reading made easy guide (pdf) and a more advanced guide (pdf). Most map companies now produce weatherproof maps which have a lightweight protective coating; very handy indeed when exploring the Lake District. The weatherproof maps produced by the Ordnance Survey are known as Explorer 'Active Maps’. The OS split the Lake District into four regions, NE, NW, SE and SW, allowing the areas to be shown in more detail. A useful single and central map is the Lake District Mountain Map by Harvey (also waterproof). With its smaller scale, it allows you to get a better understanding of how the Wainwright fells and ranges fit together.
Waterproofs & Extra Clothing
The weather in the Lake District is well known for sudden changes and a set of waterproofs should always be in your rucksack. They are lightweight and shouldn’t take up too much room. Extra clothes are a good idea; it may be lovely and sunny on the valley floor but there could be a minus wind-chill up top. A hat and gloves can help protect you from the biting winds. Worst case scenario might see you hurt or stranded out on the fells and that is when you’ll need to keep warm. Think before dismissing those extra layers from your pack.
Torch or Headlamp
A good torch or headlamp is essential even for those planning the shortest of walks. A torch or headlamp could be a lifesaver if you find yourself lost or hurt on the fells and night time falls. Don’t forget a spare bulb and batteries too.
First Aid Kit
There should be a first aid kit in some form or another in everyone’s pack. Plasters and bandages are not native to the Lake District so include plenty of those. Taking a First Aid course might be something else to consider; it could be a life saver.
Extra Food & Water
These are two items that should never be overlooked. There could be many reasons why you might have to spend longer on the fells than anticipated. Foods such as chocolate and Kendal Mint Cake take up little room and provide a good source of energy. You should carry enough water for your trip, plus extra for emergencies. How much you use will depend on you as an individual but always try to take more if you can. If you are drinking from streams take water purification tablets with you and maybe a filtration pump.
You should also consider carrying:
Whistle - perfect for attracting attention.
Waterproof matches – provides both heat and light.
Mobile phone – for emergencies only, not calling your friends atop Scafell. Mountain Rescue is obtained via 999. Don't forget a spare battery.
Sun protection – sunglasses and sun block, especially at high altitudes.
Swiss Army Knife – lots of uses, little space.