1. Rain/Sand cover. This is a really great item to pack in your bag, and simply leave there. Most are plastic and fold down to take up virtually no space. I love these little bags, because while they are designed for photographers shooting in rain, or humid conditions they also make great added protection around the pool, lakes, and ocean!! Protecting your camera from water is HUGE! Nothing fries out electronics faster then water! Except possibly sand! I couple of little sand crystals in your lens (Dslr, or point and shoot alike) and your looking at some $$ for repairs or possibly purchasing a new one all together!
This little bad boy can be found in many forms from Amazon or your local camera shop. The plastic covers aren't really made for long term use, but with care you can get more then your monies worth since they start at only $6!
Now, these are designed for larger slrs... they would work fine for bridge cameras with lens that extend out... but they make them for point and shoots, as well as other electronics like ipads, phones etc. Just remember your looking for a bag to shoot with, not simply something to protect from splashes... if you have to take it out to shoot, it wont help!
2. Silicon Packs. Crazy right? But save those packs you get with new shoes and drop a few in with your memory cards, and around your camera bag.
Believe it or not, they do help draw some of the moisture away from your electronics. If your going (or live) some place with a lot of humidity, every little bit helps! You can also pick up a handy product like Nikon's 8073 Fog Eliminator which you can wipe your lens with and it keeps them from fogging up in the humidity! Some work better then others, personally I have had good luck with this one!
3. Backups and Storage. Memory cards are a no-brainer these days... you always want to have more then you think, and personally I suggest you never shoot a whole vacation day or event on one card. Cards can get corrupted, and are prone to static shock... so I swap back and forth between several cards so if one has an issue - I still have images on another card. While that increasing my time slightly for separating them on my computer, its time well spent in my opinion. The first time you have to pay $300 for image recovery due to static shock you will thank me too!
Now backup isn't simply extra cards. I suggest if your doing more then a day trip you think about a portable hard drive, or lap top as a backup as well. I DON'T suggest that you delete the images from your card.. but simply have 2 or 3 copies as your traveling. You can pick up a 1T drive, that you can hook up a card reader via USB to for under $100 - the larger the drive the more $$ it will cost... but to me, not losing my vacation images = priceless! While your at it, pick up a nice hard, travel case for this device - they start at only $8!
4. Memory Card Storage Case. I don't trust the little pockets in my camera bag for important small things like memory cards! I suggest you pick up something like this:
This hard case, can be found in a water-tight (sand proof) option also. It protects your cards, not just from static, humidity and those types of things.. but its a great investment to keep your cards safe at home, and while traveling. Losing a card would be FAR worse then having to hassle with image recovery! They aren't expensive and in my book its just as important as my camera bag itself!
5. WIFI booster. If your traveling and expecting to be able to post images along the way, or utilize online or cloud storage sites for backups, this little guy is fantastic! On twitter the other day I was complaining about my WiFi not reaching the pool... and a friend suggested this. I was like "OH DUH!" so now I get to work while my daughter swims this summer! Perfect! It's also super handy for poor connections at hotels, or other more dodgy options such as the local coffee house. It is a super practical purchase for anyone using a WiFi while traveling... and I find it a great goody to keep in my camera bag for the "just in case" moments!
I hope you have a FUN, and SAFE Vacation season! I can't wait to see your memories!