Often some of the people who have upkept traditions have also been the poorest. And what they had to give the spirits is often telling. We seem to have an expectation today that you must get fancy expensive things. When in reality there have always been folk practitioners, and they have long given gifts to their spirits that match their station.
Some of the most popular gifts for folk to offer their spirits are as follows:
Music: this can be as simple as playing on a harmonica (a very affordable instrument, mine was 3 dollars), a small drum, clapping, singing, or even lovely recorded music.
Moments of silence: a bit opposite, but powerful nonetheless. Taking a few moments to just dedicate your focus and thought to the spirit is a lesser known, but time tested dedication to your spirits. From meditation, to just a moment of stillness during a busy day, this is a very meaningful offering.
Poetry: read, recite or compose poetry to the spirits. For most well known spirits (read gods) there is already a body of literature out there for them. Often free online (like at scared-texts.org). You can copy it out nicely and put it on the shrine for them, you can read some aloud to them, memorize it and recite it. Or if you are so inclined you can write something new for them or adapt something for them.
Incense: sometimes this can be expensive, but often it is not, some times you can get a pack of a dozen incense sticks for a dollar. Burning a little incense even just a part of the stick is a very traditional offering to spirits. They like the scent.
Water: there are a number of spirits for which a clean glass of water is a lovely offering. In some traditions water is left for ancestors, for example. Desert gods probably would cozy up to some aqua too.
Art: If you can draw or even trace something special for your spirits or gods, it can be much appreciated. If you are so inclined, most families have those water-color kits, markers or crayons. You could color in a coloring page that fits or even do something somewhat abstract or pattern based if you like to play with colors but don’t feel confident drawing something your own.
Compost: If your spirits are land spirits, garden spirits or earth spirits, conscious donations of compost to the earth are much appreciated. Much of what many people throw away, can enrich the earth. This is not the same as giving the spirits scraps, it is actually making compost for them doing the whole composting process which benefits the soil, plants and animals of your area.
Dance: If you like dancing, many spirits and gods like dancing. A lot of energy is raised dancing and it can be shared with them.
Praises and prayers: Just stating plainly and aloud to the spirits that you appreciate them and are grateful to them is big. Even better is telling their stories to people who want to listen. Telling about the feats achieved by a heroic spirit carries on their legacy and that is no small thing. Many of these stories are free to read online.
Computerized shrines: tumblr blogs dedicated to a spirit, a screen saver on your phone, and such things are good ways to keep the spirit or god on your mind. Pretty pictures, poems and writings shared on a blog or facebook page are not only good for the spirit, but also enrich the community of others interested in that spirit, the building of community also being an offering.
Games: many spirits and gods are recorded to have a love of games. Playing games like checkers, chess, cards, and even physical games like tug of war can be dedicated to please spirits and gods. Ever thought about the lore of challenging the grim reaper to a game? He is just one example of spirits who like games.