under one's belt (in one's possession; as part of one's experience)
have/get something under one's belt (to have achieved something useful or important) — иметь что-л. в прошлом; на счету; за плечами
Example 2: He's got a war and famine under his belt — У него за плечами война и голод.
Example 3: With four years of war under his belt, he seemed totally unembittered at his lot. — С четырьмя годами войны за плечами, он, казалось, совершенно не роптал на судьбу.
Example 4: If Mr Obama is able to get some early legislative wins under his belt, however, then federally-recognised civil unions for same-sex couples and immigration reform could well be on his agenda before too long.
(Story from BBC NEWS)