solemn promise to iomedae - any nice idea?

[Maculosa]

I'm playing a Paladin who worship Iomedae, lately some priest of a Iomedae temple gave me an artifact (it's a custom artifact based of the morrowfall) but in order to use it i must made a solemn promise to iomedea. the solemn promise is something that will happen when the sun is up. I must choose which solemn promise i will do. DM suggested me thing like "will not eat when sun is up" but something more "cool".

I'm out of idea... any nice idea?
Thanks

PS: Sorry for poor english.

[Furthermore]

I suppose you mean "while" the sun is up. As long as the sun is up, you will do or will not do something. Must it always be a prohibition; a thing you cannot do, such as eating? That seems more Irori than Iomedae

I will watch for your messenger.
-Allows for DM plot-hooks, but you might see the messenger where it isn't. Even false assumptions could lead to further plot-hooks.

I will speak only one word at a time.
-Interesting roleplay decision, but can make communication in combat complicated. "Smite." "Enemies!" "Blessings." "Agreed." "Look! (while pointing)" I wouldn't advise this if you are the one who does most of the talking.

I will tithe my findings.
-My Paladin did this anyway. Any gold you earn during the daylight hours, donate 10%, 20%, 33% or some other amount. Talk to your DM about what would be best. I donate 10 or equivalent value of items. 50% might be a bit steep, but that would depend on how you want to go about it. Requires book-keeping, but the roleplay of giving these things to orphans or war efforts can help to make you friends as well. (Things you find at night you can keep, if you like.)

[Claxon]

Well, I dunno as a Paladin of Iomedae you've already made a very solemn promise to her. Your Paladinhood is the manifestation of this promise between you.

I would look in the Player Companion: Faiths of Purity and research what Iomedae and her faithful and base this second promise on something very specific to her faith.