Explanation:

- Generous: This term usually describes someone giving or actions characterized by kindness and willingness to give more than expected. It doesn’t typically describe a souvenir.

- Bountiful: This term implies abundance or plenty. It wouldn't typically describe the physical size or amount of content in a souvenir.

- Considerable: This means large in size, amount, or quantity. It doesn’t fully capture the concept of a souvenir being filled with a lot of content.

- Voluminous: This describes something that is very large or takes up a lot of space, particularly in terms of writing or content. This is fitting for a souvenir, which might be a substantial book or collection.

Voluminous is indeed the correct choice because it aptly suggests the souvenir is large in size or content.