Is it permissible for a government employee to keep the annual summer allowance and spend it for another purpose?

If the allowance is a grant from the employer, and there is no condition that it be spent on the summer retreat, then there is no harm in saving it and spending it in any way. However, if the employer stipulates that it must be spent on the necessities of the summer retreat, then it is obligatory to adhere to their condition. Any unspent portion must be returned to them, unless they waive their right to it.