Most of the time when darkroom equipment is discussed, it is focused on enlargers, lenses, dry mount presses, and such higher priced items. Low-tech and low-cost things are never mentioned in these discussions. Im sure that there are many simple items that make life a little easier in the darkroom.
Here are some of my favorite low-tech things:
Drafting Right Triangles. Used to help align vertical or horizontal lines with the easel blades. It can also be used to check that the easel blades are square.
Small Clamps. These are the really small spring clamps in hardware stores and spring type clothespins. The clamps are used to hold two or three mat boards together at desired angles and configurations. I found black ones and others could be painted. The clothespins (spray painted black) are used to hold larger burning/dodging sheets. If I want to burn the sky, I may use a rejected dark print and cut the shape needed to match the skyline. These sheets can be hard to keep flat during the burn so I have a heavy mat board with a large cut out. The clothespins are used to hold the sheet flat against the mat board frame.
Rejected Prints. Besides the use for dodging and burning mentioned above, I have one other application. It is a common practice to use the backside in the easel for cropping and focusing. I also mark a scale in fractions of inches from each edge. I have a nice Saunders easel but I find the printed scales on the easel are not precise enough to get even borders. The marked scales on the rejected print will align each edge much better and will not interfere with its use for cropping and focusing. I use this print until it becomes too dog-eared and hard to insert in the easel then I just make a new one.
Blue Painters Tape. This can be used to secure a large number of items such as dodging and burning tools. The better tapes dont leave a residue and if removed within a reasonable time will not tear matt boards and such. I also cut it into small points and place them on the easel blades to help identify the start/stop locations for burns for faint images.
Florist Wire. Very narrow and dark which helps in dodging. Its only weakness is that it is so thin it will wobble and prevent steady control on a dodging shape even with short lengths of wire. Since any two points are along a single line, I have used this wire to hold two dodging shapes on a long piece of wire and dodge two locations at once. The wire extends across the entire print and is held with both hands. Short pieces can be taped to flatten and reinforce projections (such as trees or buildings) in the horizon/skyline shapes for sky burning when using rejected prints.
Magnets and Smaller Pieces of Mat Board. Test prints will sometime need to focus on small areas of the image. If the image is uniform, a smaller test strip will be sufficient. If there is a lot of variation in the image, Ill use a full sheet with the mat boards and magnets to divide it into smaller areas. The base of the easel is steel and the magnets will hold the mat boards in place.
Foam Piping Insulation for Sink Edges. I saw this in a newsgroup years ago and will attest to its effectiveness. This is the insulation pieces sold to cover 3/4" or 1 hot water pipes. It has an adhesive strip to keep it in place. This makes a nice surface to rest your arms when processing. It is much better than an unpadded sink edge even when rounded.
Now one high-tech item.
A light table with a magnifier on a boom-arm. This is used for:
aligning negatives in the holders for enlarging,
neatly cutting down a roll of 35mm,
reducing or intensifying negatives, and
making burning/dodging masks.