DVSA will not run a practical test without the right documents, and turning up without them counts as a failed test with the fee lost - this is entirely avoidable with a five-minute check the night before.
What you must bring
Your UK photocard driving licence (both parts, if you still hold an old-style paper counterpart)
If you have a licence from outside the UK/EU without a photocard, valid passport-style photo ID plus your paper licence
Your theory test pass certificate is no longer required as a physical document - DVSA checks this electronically, but it is worth confirming your theory pass has not expired (it is valid for 2 years)
The car
If you are testing in the instructor's car (the usual arrangement), the instructor is responsible for making sure it meets DVSA's requirements: valid MOT, tax, insurance that covers the test, an extra interior mirror for the examiner, and L-plates displayed correctly. You do not need to check this yourself, but it is reasonable to ask your instructor to confirm it the day before.
A simple test-day checklist
Photocard licence, packed the night before, not the morning of
Arrive at least 10 minutes early - DVSA can treat late arrival as a no-show
Glasses or contact lenses, if you need them to read a number plate at 20 metres
Confirm the pickup point and time with your instructor a day ahead, not on the morning
None of this affects the actual driving assessment, but a document problem on the day is one of the very few ways to fail before the test has even started - eliminating it in advance is the easiest preparation you will do all week.