I got my is350 shift **** for $20 in the classifieds section.
I wouldn't waste a $100 gift card on that, stealership will gladly sell you a $20-$50 shift **** for $100 no problem...
I'd use the gift card for oil change
$100 is good enough for at least 3 oil changes (assuming lexus charges under $40 for oil change)
Sears auto gift card, hummm looking through their online site, I don't think would put anything from sears in my car. That's just me though. But yeah floormats is a good idea, or try to get some tools, does it have to be from sears auto? Maybe try to get stuff from the tool section. Actually i see you can get air intakes and some stuff like that.