as far as finding things for a sp package i have found cookbooks, craft & quilting books, craft kits at estate sales. there is also fabric & threads but i miss those items because i work. one estate sale ha 3 large jars of buttons but i missed them. check clearance aisles in the stores you shop for some surprise finds along with the usually suspects: joann's, hobby lobby, tuesday morning, walmart.
i was in a walmart recently and they were clearancing fat qtrs for $.25 $.50. the fabric was a bit thin for my taste so i didnt buy any but maybe for others the fabric would be okay. my local culinary store has free recipe cards for the special food tastings they have each week. check your local store. there are free recipe books that you can order online from many of the big food companies. there are a lot of free things to be ordered online if you have the time.
these are just some ideas that may help. also when shipping try using the regional A/B priority mail boxes and see if the shipping costs aren't cheaper than using the flat rate boxes. i can usually cram a regional box full for half the shipping cost of a flat rate box.