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 Alford downstream where the river deepens, 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. Above Strathdon, 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.
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.
Trout fishing on the Don can involve a fair amount of walking and weather in Aberdeenshire can be changeable even in the summer months. Moisture wicking layers that can be removed or added to are the best bet under waders and a wading jacket that packs away into the pocket of a chest pack or fishing vest can be really useful. It is always worth having a change of clothing stowed in the car in case the worst happens as you take a dip whilst fishing!
Polarising sunglasses with an amber lens are the best option for Don fishing in all but very low light conditions. A good pair of glasses will not only help you spot fish in areas where this is possible but they allow you to see the bottom clearly when wading. For low light conditions and evening fishing a pair of polarising glasses with a yellow lens will offer an advantage.
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, this should be rated 150N or greater to be effective if the worst should happen.
Net bags must be of the knotless type, and preferably the fine mesh type as used by coarse anglers as these cause the least damage to fins. I use a net with a built in weighing scale, when I land a large trout I like to know exactly how large it is, a tape measure is also very useful and don't forget the waterproof digital camera.