As far as your drum kit is concerned, everything has to be perfect. You can't be worrying about it on stage. Are the heads in good condition, and broken in a little if new? If I'm re-skinning the kit before a tour, I put the new heads on, tune them and leave them for 24 hours. Then I'll go back to it, tune them, play them, tune them, play them and repeat this process until they're holding their tuning. This can take a few hours, a couple of rehearsals is good if possible. I'm lucky that in the Jamie Lenman band our guitarist is Chris Coulter who's an ace producer, if they don't sound great he'll soon be on the case. Lug locks can be useful for keeping the drums in tune through your set but remember your drum sound also depends on the room you're in which can change dramatically between venues. If they're all locked up that can be an added hassle in a soundcheck when people are waiting. O-rings, Moon Gel and gaffa tape are all great options to help you control your sound - it can be pretty stressful when your floor tom sounds dodgy and everyone is expecting you to fix it - everyone can hear you trying too! Make sure you have a spare set of heads (even if they're your old ones) and a spare snare onstage.
A drum mat with markers really is an essential bit of kit. You may have 15 minutes 'til doors open and you're finally allowed onstage for a line-check, knowing how much space you need helps everybody, plus your kick won't go "walkies", a horror we've all experienced at some stage. I've also found at some festivals the drum risers can be pretty wobbly so my snare and rack tom (which is also on a snare stand) have been moving around during the set. You can tape them down, but Baskey make some mat markers that will hold the stands in place which I've found to be a really good solution. As for the kit, the shells aren't really an issue if they sound nice, but the hardware needs to be durable. The top of the line stands might feel like a ball and chain at load in but you won't regret it in the long run, and they'll last a lifetime. For touring, spend your money on the hardware. Spare felts, cymbal mates, tension rods and all the other spares will come in handy. Sharpies and gaffa tape become currency on tour, keep them close and your band members closer! The most handy bits of kit in my experience are a torch, drum key, bottle opener, Sharpie and gaffa tape. Generally you need to be ready for a rush of activity in getting on stage, then getting off and packing down. The more idiot proof your kit can be the better, memory locks and colour coding stands is always advisable.
Everyone is different, but I like to get as much stuff done as early at the venue as possible. That way there's less to worry about as the stage time get near. Get loaded in, and get your gear set up, even if it's offstage. Make sure your water/beer/brandy glass of brown M&Ms have been supplied. Work out where your merch is going. Once your in the venue, it's all about being ready when you're asked.
It depends on the gig, and where along the tour I am but generally I like to have a decent warm up where I go through some rudiments on my pad early on in the day. Nearer the stage time I hit the pad again but I'm thinking more about hitting it like I'm about to hit my kit, which is a lot harder than it is when I'm going through //Stick Control//. Those are the last moments to gather your thoughts and hit the stage. I find it important at this point to focus on the show, whatever has gone on all day is ultimately leading up to your set, this is the important part! Clear your mind of anything else and go and enjoy it.