Last month, I wrote "In place of cheap church gear" and now let me suggest you use an old Dopp bag (or Dopp kit, or shaving kit) to keep your portable communion kit. The kit itself can be assembled from Nalgene-type bottles for the bread and wine. The other vessels (and linens and candles, if any) would depend upon your tradition. (I will have one suggestion for the free churches later.) A Dopp bag can carry all of these plus a small service book, orders of service or both.
Why? Because they're a handy size, "read" as a case, and are easy to come by --indeed, you may have one or have one given to you. I own three, including a grandfather's leather kit which -- apart from the sentimental value -- has the added feature of being firm-sided to protect the contents. Dividers, sewn from sturdy cloth, or fashioned out of foam rubber would keep the individual pieces from jangling if there aren't linens enough to meet this need.
Don't serve communion? Consider a Dopp kit for storing and carrying the candles and bobeshes (protectors) for a candlelight vigil or Christmas eve service.