Using the term “sell” in connection with “suggested donation” is inconsistent.  It is either a donation, in which case I can get the merchandise without making the suggested donation, or a sale, in which case I have to pay or you won’t send it to me. 

If it is a donation, which seems unlikely, you have to follow the “quid pro quo” rules and may have to notify the “donor” of the value of the merchandise that reduces the deduction for the contribution.  (See Ready Reference Page:  “Charities Must Set Value on 'Quid Pro Quo' Gifts.”)  If it is a sale, you have to determine whether the merchandise is related to your religious mission.  If not, it may result in unrelated business taxable income (See Ready Reference Page: “Nonprofits Often Worry About UBIT.”), and “too much” unrelated business taxable income could cost you your exempt status.  If you are selling related materials, however, you have no limit on the amount of income you may earn.