I like air fried chickpeas and/or edamame. They get wonderfully crunchy

salted nuts, pickles

Puffed rice with butter and salt can feel the same, but is a little more labor intensive.

Alternatively if you're getting out that much oil anyway, Chicharrones de Harina has even more crunch and is much better if you want an alternative to flavored popcorn (not that puffed rice can't be flavored, but it works better with sweet flavors)

Get an air popper. Popcorn kernels are cheap.

(Your question is a little confusing. If you're looking for an alternative to bagged popcorn, then air popper. If you're looking for an alternative to popcorn entirely then I'm out of suggestions.)