Man, this thread in it's own right has got those chase feelings going! For me, here in the UK, there are several 'markers' which mean chasing is approaching.
I guess one is our annual spring conference for the severe storm group I head (TORRO) - other chasing friends are there too and we gather in the pub afterwards, have a few beers, and look forward to the upcoming trip. It gets the excitement levels up, and it's always cool to think the next time I'll see these guys will probably be if we meet up on the Plains at some point.
Then there's the packing and list making - I'm not usually very organised but when it comes to chasing I have my list and everything gets triple checked! That's part of the fun!
Of course, the flight over is the biggest part of it all - almost 10 hours, but it's all in anticipation. As the plane races south-eastwards across the Midwest and down to the eastern Plains I peer out of the window at the increasingly flat terrain, and spot landmarks such as Old Man River snaking its way southwards. Then there are the big lakes north of Dallas as we come in to land at DFW - if we're flying south it means the southerly return flow is in residence! I've had a couple of northbound landings, which is always more disappointing!
There is a big glass sculpture-type thing at DFW on the way to the car rental place. This, perhaps, is the first true landmark which confirms our arrival in the Plains and it's time to start chasing.
Beyond that, the morning wake up and early cup or two of coffee is the real memory-jerker - just the smell of fresh coffee puts me back on the Plains! I started drinking coffee whilst on my early US storm chasing trips (I was a staunch tea-only Brit beforehand!). Other experiences are very similar to posters above, although I'll throw the hot tub and pool in there too, as I like to try to use those as much as possible!