I have never been terribly fond of the greeting card industry as I feel like it is just one more way for us to detach ourselves from genuine connections to our loved ones. I just don't understand the sense of obligation to send a generic, mass produced waste of paper that required no thought. I get really irked when people merely sign their name and don't even bother to write a personal message. If you don't know someone well enough to write a heart-felt letter then save the paper and postage. I understand greeting cards were made for the busy and creatively challenged, but the least any one can do is choose a card with personal meaning and write a quick, but meaningful note.
To remedy the tradition of receiving and quickly disposing of generic cards, I hand-make almost every card I send through the mail or with a gift. This does require more time from me, which often means that extended family and friends don't receive a card for every occasion, but I feel like the ones I do send are infinitely more worthy of the paper, time and energy put in.
It has taken time to collect a healthy supply of scrapbook papers, embellishments, stickers, fancy pens and other ephemera, but it helps the creative process to have things on hand and not need to rush off to the craft store. I like to look for whatever discounts I can find when I am out shopping, so that when I get inspired or an event comes up that I have lots of treasures to choose from.
There are several things I can't live without and always make sure I have stocked:
The Glue Lines and Photo Corners help mount papers flat, and without worrying about oozing liquid glue smearing or tearing paper. Glue lines help mount ribbons too. Decorative scissors are good for adding texture to pictures and papers, and hiding crooked lines. Distress Ink used with a sponge or foam brayer also adds interesting texture and can make pre-made cardstock cards look antique. Paper scraps are essential for mounting pictures and words. Use contrasting colors and patterns to add creative flair. These are just the basics but definitely standards in my craft pantry.
Combine these with photos, printed images, magazine pictures or any other creative findings, and you can create many different kinds of cards for all occasions. Remember the most important part is that it be meaningful to you and the recipient. If it is sewing you like then add scraps of cloth. Use what you have around the house and remember to have fun.