Using whatever shelf, cabinet or table is on hand should only be a temporary measure. Inexpensive Black MDF and steel on-line catalog stands are normally clunky-looking 4-shelf fixed 8" spacing designs and not engineered with any sonic benefit in mind. Better equipment racks and speaker stands set off the design and finish quality of your audio components while offering sound quality improvement. If audio components that put out a lot of heat are not well ventilated, board components will prematurely fail.
At kemela we are always breaking down and rebuilding stands in different configurations as new gear comes in. Modular rack systems let you design your own shelf spacing for your components and configure for the right height and efficient vertical or horizontal footprint with enough space for all your components. Better materials and styling are used and they are tested with HiFi components to see how design can help sound quality by controlling vibrations and resonances that can add frequency specific colorations to the sound from sympathetic vibrations of component boards, volume potentiometer spindles, transformers etc. Some racks can have optional castors installed which make it easier to get round the back and make changes to the cabling.
For speakers that need them, don't skip on a good speaker stand to ensure the speakers are at an appropriate height and distance from the rear wall. Most "bookshelf" speakers will sound better on a stand rather tucked away on a bookshelf. A heavier stand is better than a light-weight one that may rock when reproducing low frequency information. Stands also act to drain away cabinet vibrations that otherwise compete with the subtle movements of the loudspeaker cones causing irregularities in amplitude and timing response that can veil the midrange. Floor standing speakers often benefit from being placed on vibration absorbing wood or stone slabs.
Looking for something better to store your vinyl records in than a plastic crate? Warped records can result from poor storage and keeping records tighly together keeps out dust penetration as does cabinets with doors.
Unless the turntables have a sophisticated suspension system, most of the lower and medium price ones are greatly affected by what they are put on. For rooms with bouncey floors, other than floor joist reinforcement, a turntable wall bracket may offer a solution.