While outdoor food offerings can certainly be left on the ground, tucked into the roots of a tree, or left on an offering stone, sometimes it's nice to do something a little different. It's easy to craft little bowls to leave offerings in, bowls that you don't need to worry about finding again to pick up.
Simply take an apple, cut it in half (on the horizontal, so the two halves will sit up), and scoop out the core - being careful to leave a bit on the bottom. There's your bowl! Fill with your offering, and place outside. These are best for offerings you're going to leave close to home, but if you're going farther you could bring the whole apple and cut it at the site.
Other things you could use include miniature pumpkins (or even pumpkins that are a little larger, for bigger offerings), and gourds which are readily available around this time of year. Turnips also work well, but they can be a bit harder to carve. These little bowls become part of the offering.
Do be careful what you choose to make your bowl from, and what you leave as an offering in it. It's very likely that the local wildlife will be finding these little offerings. You don't want to leave out anything that will be harmful to them.