While this may be a total surprise, when someone takes the time to host a party, and invite you to said party, you are expected to arrive with an item, a gift if you will, for this celebration. A considerate offering of thanks for planning, cooking, cleaning and inviting you to this is party, specifically for the person(s) who invited you, is a nice gesture you can offer in kind, hence the term “hostess gift."
Equally important when arriving at a party with a hostess gift, is for you to be a self-sufficient guest. If you bring a bottle of white wine, put it in the refrigerator or in an ice bucket, especially if it was chilled when you arrived. You can even do one better and offer to go ahead and open it. Further, inquire if you can fill a glass for a few of your fellow party attendees as well.
If you brought red wine or mixer, take this opportunity to place it in the designated bar area. For the guest who brought chocolates or dessert, those can most likely be set on a counter. Simply arrange the items where it looks like other sweets are congregating. Conveying to those in charge that you assisted in this way will not only suffice, it is greatly appreciated.
If you don't drink there are plenty of non-alcoholic options to quench your thirst and those others attending who might not want to imbibe. I recently hosted a bridal shower at my place. A dear friend (who does, in fact drink alcohol) brought a 12 pack of the most yummy grapefruit seltzer. It multi-tasked the entire day, filling champagne flutes, acting as a mixer for mimosas and generally enjoying out of the bottle.
Finally, if you brought flowers, food, or maybe a special present, offer to the host(ess) if you can go ahead and place them where he or she would prefer. Ask where to find the vase, get it, fill it with water and arrange the flowers. Then clean up any ribbon, plastic or spare leaves so that everyone notices the lovely bouquet, not the garbage left from “helping” the host.
While all of this may seem like work on your part, think of it as filling the role of a responsible adult and friend. These kind souls invited you to their home. They are busily prepping items for fellow party attendees and trying to make sure that everyone, including you, has a nice time. Your assistance is appreciated. To be honest, an upstanding adult and friend needs to do their part to help and be a good ally.
There are plenty of websites equipped to help a party guest discover exciting contributions for the host of a party. One caution, however, is to make sure you give something that will be appreciated. You are attending a party and your host(ess) is creating a party atmosphere. A bottle of wine, flowers, side dish, six-pack of beer or anything that will be utilized at said party will be most valued. Please forego the feeling to go through your pantry and gift a jar of pickles, or olives, or capers. Though if you are attending a bbq, and those pickles are absolutely killer, then by all means place them on a plate and gift them in order to enhance the atmosphere. Please don't set the unopened jar on a table, only to take them back home because no one knew about them, or what to do with it. For a comical read on what not to bring to a party, see my article "Don't Bring Pickles to a Potluck."
Hostess gifts are a thoughtful way for you to let the inviter know you are flattered they included you in the event. So bring a considerate present and have some fun. The reality, though, is that it's not the present that's important. It's the way you assist in executing the proper use of your gift that truly makes a positive impact. And parties are supposed to positive, right?