Every week, Mr. Tanaka saves a little money just in case.

Literal

Every-week Tanaka [topic-は] just-in-case [purpose-に] prepare little-by-little money [object-を] is-saving.

万一に備えて ('in preparation for an emergency') combines 万一 ('one in ten thousand, just in case') with 備える ('to prepare'). 少しずつ distributes the saving across weeks. A responsible financial habit.