Just to gain a bit of real experience rather than trying to simply memorize what a bunch of different people say (and which apparently conflicts with each other),
- take a white towel with texture, and illuminate it from perhaps a 45 degree angle with a unmodified small light source
- Meter the towel with your camera in Partial or Spot mode, and the resultant suggested reading will record your white towel as dingy gray (18% tonality)
- Now take a series of photos in perhaps 1/2EV increments: e.g. +0.5, +1.0, +1.5, +2.0, +2.5EV, +3.0EV, +3.5EV
Now in your PC examine the resulting photos and determine which of the above 8 shots results in
- just perceivable detail in the towel
- no perceivable detail in the towel
And now you know that for THAT type of lighting where to target your exposure...AT (or a small fraction below) the 'perceivable detail' detail step...the no-detail is totally blown out and useless for what you need to do! If your lighting is less contrasty, or if it is at a different angle to the towel, the threshhold of detail will be different. So if you still see detail at +3.0EV above the '18% gray' reading of the towel, you can try to shoot and chimp photos of some of the actual items, to verify that you capture and see the necessary detail in your tone-on-tone item being photographed.
Also keep in mind a fundamental principle...if you light your subject with ONE light, and the illumination from that light also falls upon the background, the background will not be 'as bright as' the main subject when it is any distance farther
from the light source. So even if your rope bag was identical to the backdrop in inherent tonality, the backdropwill be somewhat darker than the bag and 'separated' from the subject by the tonal difference (I am assuming the bag is not literally laying upon the surface of the backdrop) .