Attached to the back of my pack is a trusty plastic trowel, which we use to dig six-inch holes for pit stops. It also houses my whistle and has duct tape wrapped around the handle. We figured the poop shovel was a good home for the whistle. When you set off to use the shovel is the time that you leave your pack behind and venture off the trail, a perfect opportunity to get lost. Blow the whistle so your companion can find you.
Plastic is lightweight but expect the trowel to break easily.
Ours is a stubby version of its former svelte self. A metal trowel would last longer and dig holes better, but it would also add weight to your pack. There's always a trade off. The duct tape around the trowel handle softens the grip and comes in handy for any type of repair. We've used it to bandage feet, mend a tent hole, tape a torn map together, etc.