Simplest is white, Matt black, both a crumpled and smooth aluminium/mylar and, some gold material, glued down to card card or foam core sheets, large home built 'wall' reflectors and small white & black index, etc cards for shelf/table top sets.
Curtain sheers, black and white are good for 'conditioning' incoming light, especially before being reflected into a shot, but bed white sheets work too.
Reflectors in black, 'absorb' light from, for example the dark side of a person's face, white/silver/gold, kicks it in.
White cards need to be actually white, and, besides top notch white 100% gotten rag art papers good, heavy pigment paint, Tin. Is great, lead will gray, and zinc is transparent, so it needs a number of coating, for a 'glow' effect. It's also sort of blueish.
You can also try diffusing through thin 'kozo' papers, in multi-coloures and some in patterns or with inclusions
Small flash units can be hidden in the scene, medium and large units can be directly pointed through sheer materials or reflected in by umbrella, card, wall.
These are good starting tools, used by many photographers and should keep you busy learning how versatile they are, for a long time.
Most important, if doing b&w, colour contrast, warm-cold contrast, reflective-matt contrast, etc, will always matter too and never forget, white on black, black on white is always key in setting up your 'set'.
IMO.