A cabinet shelf is one flat plane, but most cabinets have the height for two. The trick isn't building — it's hanging a basket under the shelf you already have, so the air below it starts holding things. A slide-on under-shelf basket does exactly that: it clips on, needs no tools, and turns single-shelf cabinets into double-shelf ones the same afternoon.
Why slide-on beats build-in
Adding a fixed shelf means brackets and measuring and a drill. A slide-on under-shelf basket ($27) hooks over the front and back of the shelf you have and stays by friction. Because it expands to fit, it meets your shelf width instead of leaving a wobbly gap. One clip and the dead space under the shelf is storage.
What to keep in it
The basket is best for the light, daily-reach stuff: tea bags, snack packs, spice backups, the wraps you grab hourly. Keep it shallow-load so the shelf above still closes, and group by category so the next person finds the thing without unpacking three containers. A labeled basket beats a jumbled one every time.
See-through so you stop rebuying
Steel wire shows the contents, so the backup jar of something is visible and you stop buying a third. Opaque bins hide duplicates; a wire basket keeps them in sight, which is the quiet way a cabinet stops overflowing. The back row stays reachable because you pull the whole basket, not one item buried under others.
Add a pull-out for the floor
If the cabinet also has a deep floor, a pull-out drawer basket ($30) handles that while the slide-on handles the shelf above. The two together use nearly the whole cabinet height — shelf tier plus floor tier — without modifying the box.
Double your shelf: shop the slide-on basket or see the Cabinet set.
The slide-on basket isn't the only clip-on option. Four other no-drill ways to use the same cabinet include an under-cabinet rack and a hanging tier, both of which skip the drill.