Any rod between 9 and 10 feet rated for lines 4 to 5 is generally considered ideal for trout fishing with conventional tactics on the Don. The longer rod can be advantageous from downstream where the rivers deepen, widens, the banks steepen and it is often necessary to fish through walls of reeds, particularly in the summer months. A longer rod is also advantageous for holding line off the water and mending to reduce drag on some of the deeper eddying pools on the lower river. In the head waters, a shorter rod may be of some benefit as the river here is small and a long rod can often be a hindrance.
Stiff, fast action rods do not give much of an advantage on the Don as most fishing is done at close range; stealth and presentation is much more important than the ability to cast a long line. However, your chosen rod should be responsive enough to allow curves, mends and slack line casts to be thrown with accuracy where required. Ultimately, the angler should fish with something that they are comfortable with.
When conditions are hopeless, or for late evening fishing in the summer and autumn, it is definitely worth having a second rod that will cast something big on a sinking line; a 6 or 7 weight rod lined with a fast sink shooting head that will carry a large streamer is very likely to put you in contact with some of the Esks Seatrout.
A typical Border Esk seatrout.
For standard trout methods (dry, wet, and nymph) a fairly short headed WF line is ideal as you will rarely be fishing with more than about 30 feet outside of the tip. For the occasions where a long cast is required a WF will give an advantage as there is very often not the space to aerialise a long length of line; the ability to shoot from a short cast is a definite advantage. Whatever line you use, make sure the tip floats high, this is vital for detecting subtle takes when fishing subsurface and avoid braided loops as they can cause all sorts of problems with presentation, a tapered leader is a solid choice. For streamer fishing the best option is a fast sinking shooting head. This can easily be made from 30' of a cheap fast sink DT line two sizes heavier than your rod is rated, use 30' of DT8 on a rod rated #6, or 30' of DT9 on a rod rated #7 etc. The head should be connected to a floating running line either of the coated fly line type or one of the hollow stiff mono lines.
Ultimately it's there to hold your line, so any modern fly reel is fine for trout fishing, huge drags are not required - even for the largest of trout! A large arbour offers an advantage over traditional reel types as the line is stored in large coils and comes off the reel with less memory. If you need to get line back onto the reel quickly a large arbour will do it faster than a traditional reel. However, many anglers do prefer older reels and provided it's in sound condition it's down to personal choice.
Tapered leaders are essential to ensure an accurate delicate presentation of the fly. Carry 7.5', 9' and 12' leaders tapered to 4X diameter, these should cover most situations. Tippet material in 4X to 6X diameter should suffice for most methods and flies you are likely to need during a day out on the Don. Stiff fluorocarbon material in 0X or 1X is ideal for streamers.
Chest waders are almost essential on most beats of the river. Breathable stocking foot waders are the best option as these allow the angler to choose a supportive boot with a sole that suits their needs and enables the angler to layer up underneath as required.
Felt soles provide the best traction and are by far the most stealthy once in the river but can be lethal of slimy rocks or wet muddy banks. The new generation of sticky rubber soles are better on a wider variety of surfaces but not so quiet on the stream bed. Banks on the Don can be treacherous and wading can, in places be slightly interesting.
A wading staff is essential and should be worn on the downstream side fastened in such a way that it can be jettisoned if it becomes jammed between rocks, never slung around the shoulder or neck. A life jacket is also advisable particularly when the water is cold early and late in the year or when the river is running high.