Q. Can I use a gift certificate or card to reward on Yom Tov the child that finds the Afikomen?

A. Horav Shlomo Miller’s Shlit’a opinion is that gift certificates and cards are muktza on Shabbos and Yom Tov. We could assume that this is because they constitute a monetary instrument that one is prohibited to use and redeem on those days and therefore qualify as a “K’li shemilachto l’isur,” since their primary function is one which is prohibited on Shabbos and Yom Tov. However The Rov’s opinion is that they are muktza machmas gufom. This refers to objects that do not posses Toras Keli or the use of a utensil, like sticks, stones, money, live or dead animals, broken vessels, etc..
The former muktza is subject to certain lenience, and can be moved l’tsorech gufom, meaning that they may be moved for a secondary permissible function, or mekomam, meaning they may be moved if their place is needed. Muktzah Machmas Gufo however, may not be moved under any circumstance.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a