There is no harm in wearing belts while in the state of Ihram

Q: What is the ruling on a Muhrim (pilgrim in the ceremonial state for Hajj and `Umrah) wearing a belt to keep his money safe; is it permissible to do so or is it considered a sort of Makhit (clothes sewn to fit body limbs) which is not permissible to wear?

A: There is no harm in wearing belts and the like, such as waistbands and handkerchiefs which are used to keep money and other important things. May Allah grant us success!

[Fataawa Shaykh Ibn Baaz - Alifta.net]

See Also: What is the ruling on wearing a leather belt sewn by a sewing machine and stitched shoes?