Foldy-roldy is a play on "folderol", meaning useless, added for no reason, trivial.

Pronounced "folly rolly".

"Tilly-tolly" just rhymes.

"Seek a double" meaning extra, as in double.

"Use a cause-a roll a' (of) binding." Again, a little nonsensical syllabic innovation, but ultimately Jenny is simply playing coy, not telling what color dress she'll make to wear a-courtin'.

Binding is material for hems and seams on clothing.

Fun song, and I'm endeavoring to learn it first on my new (old, used) long-neck banjo.