One of the keys to a successful party is to figure out what can be prepped ahead of time. That will make the day of the party that much easier. For example, if I do cheesecake or Key Lime Pie, they
have to be done at least a day or two in advance in order for them to set properly. Other condiments like onions, tomatoes, etc. can be sliced/cut up the day before and placed in a ZipLoc bag in the fridge. Burger patties can be formed the day before. Cookies can be baked a day or two in advance and the dough can be made a week or so in advance if tightly wrapped and placed in the fridge. Liquor and soft drinks can be purchased weeks before the party. Ice is usually the big bugaboo since it you need much more of it that you normally would for your usual daily routine and, since it needs to be kept frozen, freezer space is often at a premium. Therefore, that is something you may need to purchase the morning of the party. You could purchase it the day before and keep it in a well-insulated cooler, though a little bit of it will melt and you may have to drain the cooler the morning of the party. I finally broke down and bought a 5 cu ft chest freezer for about $160 that mainly serves as a dedicated ice freezer. It still has room for the ice cream treats as well. This has allowed me to buy ice well in advance and avoid any errands on the day of the party. Just something to consider - it's made my life easier.
Another thing to be mindful of...have ways to keep hot food hot and cold food cold. This means having warming trays or similar devices to keep hot food warm (above 140°F) and double-insulated bowls to keep cold food cold (below 40°F). It also means having good, reliable, and accurate digital thermometers for spot-checking food temps. As much as I like the Thermapen (retails for between $79-99, depending on the version and it's still my first choice), you can purchase a ThermoPop for about $29. The ThermoPop is about 8-9/10ths of a Thermapen - major difference is a 5-6 second read time vs. the almost instantaneous reading of the Thermapen. ThermoWorks is currently offering 15% off sitewide, so now is as good a time as any to step up to a Thermapen at a really good price (see
http://www.thermoworks.com/). Yes, I realize this is an investment. However, salmonella and his good buddies e.coli, campylobacter, and Clostridium botulinum are very unwelcome party crashers. As much as I enjoy the fond memories of several of our pool parties, the one thing I am most proud of is that no one has ever gotten food poisoning at any of our events (pool parties, SB parties, Final Four parties, dinner parties, etc.). Despite some of my light-hearted and juvenile antics over the years courtesy of the big kid in me, I take food prep and handling
extremely seriously - there is no room for error.
If anyone is interested in a deeper dive on food handling and the science behind the more common bacterial contaminants and how to avoid them, check out this thread:
And now, a Few Words on Food Safety Proper Handling. One thing I will mention here for the sake of brevity and convenience, do not keep baked potatoes in foil to keep warm after they have been baked. This has been linked to botulism! More details are available in the aforementioned thread.
Gotta have tunes on the entire time. A couple good yard games to work-up a healthy sweat to earn that refreshing pool time. 
