Presenting the hostess with a gift is an age-old tradition. It is a form of expressing gratitude for arranging the event or party. Though it is not mandatory for every event, but presenting a gift is social etiquette and a nice way to appreciate her efforts. Choose an appropriate gift thoughtfully and not for mere formality.
If you know the hostess very well, then you can choose something according to her taste. If she loves watching movies, then get her tickets to a new movie. If she is a literature fan, give her the current best-selling book. You may even go for homemade things that will surely impress her. Candles, soaps, cookies, thank you cards, etc., are great ideas. Gift certificates are always perfect since the recipient can choose whatever she likes. You can purchase gift certificates for a beauty salon, a restaurant, a coffee shop, or a book store.
A hostess of a bridal shower needs to plan so many things like inviting the guests, deciding the favors and the food, and so much more. Flowers are the best thank-you gift for anybody. You could even get her a flower vase, that way she can keep it for a long time. If she is a makeup enthusiast, you could give her a nice cosmetic bag or a cosmetics set. If she is a very close friend of yours and you want to give her something extra special, then you can go for a jewelry set. Photo frames are great for the hostess to keep memories of the bridal shower.
When you are invited to a dinner party, you must bring something to thank the hostess for the wonderful food she served you. A good wine is always a great idea. You may even think of taking a bottle of champagne if the dinner is arranged for a celebration. You can get her bottles of her favorite drink if you know what it is. If the hostess is fond of food and cooking, then cookbooks are your best bet. If you are going to stay overnight after the dinner, consider giving a tea set or a set of wine glasses. If it is a casual dinner, then you can simply bring some dessert like ice cream or a cake.
There are no specific rules, so you should present something thoughtful to the hostess to let her know that her effort has not gone unnoticed. She will be extremely happy that you thought of her.