Dull boring old thing isn't it? Looks like a cigar case. Probably worthless in terms of monetary value, but historically it's priceless.
I think this Cadburys packet goes right back to the beginnings of the firm. John Cadbury started the business in 1831 in Bull Street Brimingham, in the late 1840's he was joined by his brother Benjamin, and the firm became Cadbury Brothers, then in 1853 they got their Royal Warrent. All the packaging before they became Cadbury Brothers was marked either John or J Cadbury, or just Cadbury. This looks almost Georgian, so I think it dates from the early to mid 1840's.