The contents of each extradimensional storage space are, in turn, in different planes, so the weights of their contents do not count for the maximum capacities of the extradimensional spaces in which the containers are stored.
To make an analogy, in your first apartment you put a door to a second apartment. Inside that second apartment you put a door to a third apartment. The first apartment cares what is in that second apartment only to the extent that the door of the second apartment weighs. Similarly, the second apartment cares what is in the third apartment only to the extent that the door of the third apartment weighs. (Of course, other things can be thrown into any apartment, but those things only count for the weight of that apartment, since those things are, like the door, only in that apartment.)
Therefore a pioneer bag You can store extra-dimensional up to 10 pounds and weigh 1 pound. TO smaller holding bag You can store extradimensionally up to 50 pounds. and weighs 3 lbs. A practical backpack It can contain in its three pockets extradimensionally up to 120 pounds. and weighs 5 lbs. Combined, a user can keep within their pioneer bag a smaller holding bag within which there is a complete practical backpack.
The only real consequence of doing this is that while an extradimensional space is inside another extradimensional space, the space that is within space is inaccessible. For example, a creature can not wriggle in its celebration bag and, while inside the handbag, access there the contents of your practical backpack.
Wonderful elements in extradimensional spaces says
A series of spells and magical objects use extradimensional spaces, such as rope trick, holding bags, handbagsY portable holes. These spells and magical objects create a small pocket space that does not exist in any dimension. Such elements do not work, however, within another extradimensional space. If they are placed within that space, they stop working until they are removed from the extradimensional space. For example, if a celebration bag is taken to a rope trick, the contents of the celebration bag be inaccessible until the celebration bag it is taken outside the rope trick. The only exception to this is when a celebration bag and a portable hole interact, forming a rupture with the astral plane, as indicated in their descriptions.
Some GMs warn against putting any Extradimensional space within another extradimensional space, citing the possibility of explosive consequences. If you are in a campaign of this type, this player strongly recommends that you do not do this practice until you can verify the accuracy of such consequences. However, as in the previous quote, in most campaigns, such explosions and implosions are usually only a by-product of filling in a holding bag et al. in a portable hole or vice versa instead of nesting multiple celebration bag– Similar items.