Some of it is essential, some of it you can get by without but might prefer to have
Your flight school will usually be able to provide individual items, or may sell an entire "kit" which contains all the necessary items
The Essentials
You don't need all of these items before your first lesson, in fact most of them aren't required until you start Navigation, but do get a log book and kneeboard straight away. As you learn to communicate using the radio you'll need to jot down items to make them easier to remember and read back
Headset - your flying school will lend you a basic headset for every flight, so you shouldn't need to buy one. As you progress through the course and depending on your budget you might opt to get your own - see the "nice to have" section below
Log book - it is now possible to keep an electronic log book (various apps available), but most students prefer to have a physical book which they update after every lesson
Kneeboard and pen - you'll need something to be able to make notes on while you speak on the radio and later on to rest your PLOG on when you are navigating. A5 is a good size. Keep it simple, you don't generally need one with lots of pouches and extra bits and pieces attached. For a pen, it's best to use a simple Biro with no lid (click in/out type), and which has a clip so you can tie it to your kneeboard with a piece of string. Choose a kneeboard which has an elastic loop to hold the Biro when you are not using it
CAA Chart (1:500,000 scale) for the area you will be training in
Markers to draw on the chart like these - other brands available but make sure permanent and get several colours
Solvent to erase the pen marks from your charts. Dry board marker pens act as a solvent, you can also use isopropyl alchohol or nail varnish remover with a tissue, just don't bring bottles of it in the aircraft!
Protractor to measure angles on the chart, similar to this - the square version is handy as it also serves as a ruler
Scale ruler for drawing lines and measuring distances on the chart, similar to this
Flight Computer, affectionately known as the whiz-wheel. It's a plastic device which is used to calculate among other things wind drift and adjusted headings. You must use this for calculations during the navigation written exam so it's best to get used to using it before the exam. They are easily available second hand as well as new
PLOG sheets (Pilot's Log). These are pads of pre-printed sheets which provide a template to fill in when planning and then flying a route. You can make your own, or use one of many different types available like these Don't get anything larger than A5 size, and they should fit your kneeboard
Timing device - a wrist watch, stop watch, or anything which can easily give you the time, including a second hand or counter. Everyone has a personal preference - you'll probably need a bit of experimentation to determine what works for you. A mobile phone is not recommended as it is fiddly to hold and screens lock or timeout
Nice to Have
Noise cancelling headset - these headsets are expensive but an excellent investment if you plan to fly regularly. The two most popular brands are Lightspeed and Bose. Frequently available secondhand on e-bay, but make sure you get the right connection type (GA not LEMO!)
Sunglasses - although it feels like the sun doesn't shine much in the UK, it's pretty bright out there most of the time. If you have prescription glasses, you can either use clip-on shades or get prescription sunglasses. Otherwise normal good-quality sunglasses are fine. They don't need to be "aviator" sunglasses, but do choose a pair with slim legs which fit nicely under the earpieces of the headset
Flight bag - you'll need something to carry all those bits and pieces around in. Of course a plastic carrier bag will do fine, but it can be nice to have everything just where you are used to finding it without rummaging about. There are any number of "flight bags" for pilots available, but keep it fairly simple to start with. There's no point wasting money on expensive bulky items with thousands of zips and compartments at this stage. My preference is a small back pack which has three main compartments, one for headset, one for charts, tablet and kneeboard, and a third for small items like pens, batteries and glasses
As you progress or after qualifying
SkyDemon subscription - No, you can't use SkyDemon during your skills test. You must learn to navigate using dead reckoning techniques with chart and compass. Nevertheless you should be taught during training how to use and get the best out of electronic tools, such as SkyDemon, safely, with suitable fallbacks. There are other "moving map" applications such as Foreflight and Garmin Pilot but honestly for UK VFR flying, SkyDemon is the best option. I'm not a shareholder! SkyDemon
Dedicated device - some pilots prefer a dedicated device to run SkyDemon, such as a mini iPad or Android tablet, others prefer to use their regular phone. Either way, it is sensible to have a second device charged and available in case your primary device fails or runs out of charge during flight