Maybe something cute you could do if you are into crafty things, is to get a cross stitch pillow case (i think they sell for about $5 for a package of two pillowcases) and cross stitch small designs for your sorority big sister!
if you have never done cross stitching before, it is very easy and there are thousands of online sites to teach you how to do it in a flash
http://www.dnai.com/~kdyer/faqs/xsti...tml#sel_fabric
some other crafty ideas:
decorated picture frames, tote bags, decorated mini scrapbooks (for all your big/lil memories!)
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