For those of us who have had previous mcs I suspect we wouldn't dream of buying anything early. I waited for the 20 wk scan with DS1 to do any serious buying, just bought a teddy or 2 before that, and did the same this time (now 27 weeks and pretty much shopped out ).
For those lucky enough not to have had any mcs, relax, enjoy your pregnancy and shop if you feel the need. Most women, even those who have multiple mcs, will eventually go on to be successful. Keep a positive attitude would be my advice