Unless you are using wireless as part of your performance (to sync with other computers or controllers) make sure you disable the wireless functionality. Many computers will sit there broadcasting and looking for wireless connections in the background. Though this isn't so much a performance concern, it does get annoying to get popups during a performance about blah blah wireless network found. More important though, there have been AirPort updates (on the mac) which for some reason caused unstable audio. It would crackle and sizzle if Airport was turned on but play fine when disabled. The basic rule holds here, if you don't need it for a performance, get rid of it. If you're not using wireless, turn it off.
Not everyone is as good with a laptop touchpad as a mouse. Live performances with low light and sweaty hands might make your mouse dexterity less than ideal. Ever been on stage and needed to click on something across the screen but your hands were too sweaty to make the trackpad work? I have. Learn common keyboard shortcuts for your software and use them. They can save you when you need it most.
As part of your practice routine before a show, test any custom shortcuts you created. The last thing you want is to be on stage and hit ctrl+alt+n thinking it will play the next scene and instead it loads a blank file. In general with computer performances, you have to expand the idea of what it means to practice before a show. Practicing is not just about "can you play your parts" but also "will this work as expected". A bit different than how a guitar player would look at practicing.
Plan for Sweat
I know I've mentioned moisture several times now but this one is very simple. Have a towel around! Usually with laptop performances you're bending over. Sweat pouring down your face and on to your screen and keyboard isn't good for the machine or for your visibility. Even if you don't move at all on stage to work up a sweat, stage lights are HOT. In the right city at the right time of year, no matter your weight or movement you will get hit with sweat and not see your screen. Have a towel. You'll look much better in all those facebook photos people post of your show too when you're not dripping the whole time.
Plan for Glare
This is a bigger problem for outdoor performances than indoor. Laptop screens don't handle glare or sunlight well. If you depend on seeing your screen to play you may be in big trouble if there's glare. Easy to fix though, just get a laptop "privacy screen". They fit right over the screen and while they are normally sold so people can't see what you're doing if they're next to you, they also do a great job at handling glare. Think of them as sunglasses for your laptop.
Power conversion versus Power Adapter
If you travel internationally, consider that there is a difference between a power adapter, and a power converter. It is common (if you go between Europe and the US for example) to come across different voltages. A "Power Adapter" is used to convert the plug shape on your devices but normally they DO NOT convert voltages. These are usually the cheapo things you get in airport giftshops or discount stores. They allow you to physically plug your electronics into the wall in any country. However, depending on the device, you may ALSO need to convert the voltage. Many laptops are now "dual-voltage" (like Macs) so you don't need to care. But is yours? What about all your controllers and audio interfaces? Are they all dual voltage? No? Then you need to use a Power Converter in addition to an adapter! (sold separately)
Have alternate playback (ipod, thumbdrive)
What happens if the worst case occurs after your 3rd song. Your'e playing and everything is fine, and suddenly your laptop goes poof. What do you do? There is no time at that point to borrow someone elses machine, copy your files from backup and so on. The audience is staring at you. For many bands this means show's over. However you just traveled many miles to play this show. Your contract says you get paid for a complete performance. What do you do?
Some will argue that it is unethical to "cheat" and play your set back from an ipod and fake it on stage. I can't decide that for you. But you may want to decide before-hand. What if you've spent 100's of dollars to get to a show, and only get paid if you play your full set, and your laptop dies in the middle? You might consider having an iPod (or something) soundchecked and ready to rock in emergencies. If anything, maybe you play one track back from the iPod while you try to get your computer working again. Having an alternate ready to go and checked can save your show!
Don't change anything the day of the show
It's hard to say which recommendation is most important. But this is clearly one of the most. I can't tell you how many times I've seen threads on forums that start with "URGENT HELP NEEDED: I have a show tonight and ...". Many times these were caused by doing an OS, or software upgrade the day of a show. Once you practice and have all your setup solid DO NOT CHANGE ANYTHING until after the show. It may not seem like a big deal to install that "critical update" to go from Software 5.1 to 5.2 but you'll quickly learn that even the smallest change can have a big impact that you do not want to have to deal with the day of a show. Basic logic applies here. If it aint broke, don't fix it the day of (or before) a show.