I give offerings for 5 basic reasons. I'll talk about all of them, but I'm going to focus on the last kind, because it's something I haven't seen written about as much.
Offerings during ritual
Thanksgiving offerings
Maintenance offerings
Sin offerings
Hospitality Offerings (the Wet Egg)
1) Maintenance offerings. Spirits that I work with regularly get fed at regular intervals. For example, my ancestors get a candle, a glass of water, a small bowl of grain, oil and honey, and a shot of metaxa once a week. The Great Lady Undergound gets a candle, oats, olive oil, honey, and an egg every dark moon. Spirits I work with often sometimes request something else, and I usually give it to them, because I like to encourage communication. For example, Grammie (an ancestor) recently requested milk. and Helios requested...I didn't know what, so I had to get up, and stare into the fridge for a while, but he finally settled for orange marmalade. I try to "listen" carefully when I'm at the grocer, to see if I feel any odd inclinations to buy weird stuff.
2) Thanksgiving offerings. When a spirit has really come through for me, either produced something I specifically asked for, or something I didn't even know I wanted, I make an extra offering. Usually, this is a whole raw egg cracked into a glass of wine, but sometimes something else I know they like. When I compact for something, I also promise specific additional offerings when the magic "pays off". For big stuff, that's often a whole bottle of liquor poured out at the crossroad and a charitable donation to an appropriate charity.
3) Sin offerings. When I've done something I feel was wrong, I make a sin offering to the Most High which is usually a donation-purchase of livestock with Heifer International. My practice of sin offerings is strongly informed by ancient Jewish Temple practice. I sometimes also make sin offerings to lesser spirits, if I've sinned against them (by accidentally defiling their altar, or not making good on a compact or whatever).
4) Ritual Offerings. I often give offerings during ritual, these are basically bait to get the spirit to show up or down-payment for something I want. Often times, during the ritual, a spirit might request additional offerings, which I usually haggle over.
To me, a very important moral precept, perhaps even one of the most important, is that of hospitality. When someone comes to my home in need, it's incumbent on me to feed/house them. Pretty much the only thing that can excuse me of my host-responsibility is if they violate the laws of hospitality as they apply to a guest (for example, by attacking me or mine). When I was a kid, my parents NEVER would have let a guest (announced or not, friendly or not) leave without offering them food and drink. I'm the same, and I feel the same way about spirits. Unless a spirit is actively and intentionally threatening, they're welcome in my home. For me, that even extends to spirits who aren't really friendly or helpful. If they're hungry, I feed them. I only banish when I absolutely have to. (But, I'm not saying other people should do that. It's a particular calling of mine.)
Here's how I do it.
On a raw egg, I write "Please distribute our offerings to All." with a magic marker. I put the egg on a small plate. It gets surrounded by coins, beads, candies, spices, a tiny metal goat, some crystals, and whatever else seems right at the time. I pour some rum, oil, and honey over it. Whenever any offering is made in the house (and whenever else I feel like I should), the egg gets wet (with liquor or oil) first. Every few months, when the egg is light or the plate gets too sticky/gross, I throw out the egg, wash off all the non-perishables, scatter down some fruit or candy or spices and such, and pour more rum/honey/oil over it. When I used to have a yard, I disposed of offerings at the foot of a large oak tree, but now that I live in the city, I just throw them out, and I haven't gotten any complaints. The plate pictured above has been out for about a week, so it's not very cluttered and sticky yet. The mints got added just now, because I wanted to give something in exchange for the photo. Legba seemed to really like them.
The plate I'm using now is white, and painted in red with Legba's veve. It was a gift. I've never worked with Legba in any way except this, and I don't usually call him by name or reference him in any way when I work with the egg, but it seems like the plate for the job. I mostly think of the egg as being administered by a loose collection of various gatekeeper spirits including Legba, Hermes, and Hekate. The spirits that "know the name of every spirit" and "open the ways". Since the offerings are for everyone, it's not so important who does the distributing.
The egg plate lives on the kitchen "bar", which is very close to the front door of the apartment. I say hello to it when I come home, and goodbye when I leave. "Hello, egg! I had such a shitty day today. I'm so glad to be home. Drink with me!" "Hello egg! Today was great. Drinks are on me!"
I've been doing this for about a year now, and I notice real benefits. The "spirit ecology" in my apartment is noticeably pleasant and friendly. Seriously, every single sensitive person who's been in the apartment has commented on it. Also, several people have told me that I "have a lot of allies in the spirit world who I don't even know".
UPDATE: Here is a picture of the same egg after a week. You can see that the candies have (under the constant application of rum) dissolved into a kind of gross pink goo.
UPDATE: As promised, here is a picture of the empty plate. I have thrown out the egg and spices, and washed all the hard bits clean of goo. I am about to "restock".
And here it is restocked. New egg, clean coins (including 3 Mercury dimes), iron key, brass beads, all-seeing eye bead, new frankincense, star anise, and red/white mints. This time, I left them wrapped, so hopefully they will stay non-goo this time. I poured olive oil, white rum, and honey over the whole thing, and then a sprinkling of nutmeg (which is a favorite of Hermes). You can see our watch-dragon in the picture. :)
UPDATE: Here's a video about how I set the egg: http://traifbanquet.blogspot.com/2015/04/wet-egg-instructions.html
NOTE: In the video, I say "herkimer diamond", but I meant "Cape May diamond"
NOTE: In the video, I say "herkimer diamond", but I meant "Cape May diamond"