There is some need for clarification to really answer this question.
First of all, there is a HUGE file size difference between photos taken on a 16-24 mega-pixel good quality camera and an iPhone or iPad-like device. Sure, you can take many iPhone photos and upload them to the cloud or whatever and it won't add up to much space - and won't take forever over the low-cost hotel wifi system. But anyone taking photos with a large file size will fill up that space in a big hurry and definitely will encounter major frustration with wifi availability and speed. I'm no professional photographer, but I will take at least 16GB worth of photos each week I'm on a trip.
There are probably at least a dozen wifi/cloud/internet based solutions to the question you asked, but they are all subject to wifi availability, speed, and reliability. I would not go that route. The lowest-tech, easiest solution is to stick with multiple smaller SD cards and switch them out, assuring that if you suffer the 1 in 100+ chance that a card goes bad on you, you only lose a small portion of your photos. The next best solution is to download the content of the SD cards to another device you have with you. Some people use cheap netbook-style laptops (as little as $250), some opt for a much nicer computer, but still small and light, like the Macbook Air 11" ($999) and some opt for a tablet device with an appropriate amount of free memory. If you would be traveling with one of these devices anyway (as many people do), that is by far the best option.
So using the $29 camera connection kit, you can import the SD card files to your iPad and just keep them there. No need to transfer them via internet anywhere unless you envision taking more than about 12GB worth of photos and your iPad is the minimum 16GB of memory. I'll be taking a trip to Istanbul in March taking a lot of photos and my iPad (with 32GB of memory). The iPad will leave home with about 2GB worth of basics on it and about 20GB worth of movies I might want to watch. As the days pass and I watch a few movies, I'll delete them, freeing up more space for photo downloads. By the time the trip is nearing its end, I will have as much as 26GB of photos on the iPad and just a couple of movies left for the plane ride home. Of course, I'll never delete the photos from my SD cards until I have then duplicated several times at home. But saving them in two locations (SD card and iPad) while away is safe enough, IMO.