What is the ruling on going on a honeymoon, and is it permissible for someone who is unable to hold a wedding banquet to go on one, especially given that extravagance in wedding celebrations is forbidden?

It is Sunnah for the husband to hold a wedding banquet (walimah) according to his means, without extravagance, following the Sunnah of the Prophet, peace and blessings be upon him. The Prophet, peace and blessings be upon him, held a walimah for Safiyyah with what was available to him. The walimah is Sunnah according to the majority of scholars, and it is permissible to hold it after the marriage, but it is preferable for it to be held during the days of consummation. Extravagance in banquets is forbidden in Sharia, because Allah does not love the extravagant, and because the blessings of marriage come with reduced expenses. Therefore, it is recommended to hold an affordable walimah, even if by inviting a few people. If that is not possible and it is feasible to spend the honeymoon without financial cost, there is no harm. However, if there is a cost, it is better to spend a portion of it on the walimah because it is legally مطلوب (required/desired).