See if you like any of these!
Hi Shirley. You could sew them together to make a quilt. Once sewn together place flannel fabric on the other side and sew together with quilt. That will give you a warm blanket for those really cold nights.
We made beeswax food wraps out of handkerchiefs
Here are some ideas from Pinterest https://www.pinterest.com/pin/207095282851435509/
Make great throw pillows unless you mean the tiny handkerchiefs that are monogramed. I made porch cushions with mine. Use for table napkins or sew a bunch together end to end for a table runner. Cut and stitch into sachets. Make Christmas ornaments to hang on the tree cut into hearts or cute animal shapes. Sew a button for and eye. Use the small ones that are monogramed as gift tags. Cut and stitch square or circle pieces attach a piece of yarn as a handle and stuff with lavender, cloves or rosemary.
The sky is the limit on this! Use your handkerchiefs just like quilt squares or other pieces of fabric, so you can make thousands of things that are made out of it. Look at sewing books and patterns for great ideas for crafts, toys and clothing.