When we go on vacation, I want to take a laptop and a Raspberry Pi with me to monitor the outside temperature. I have a constant power supply, however there isn't a network or internet connection. What is an easy an reliable solution for sending the temperature data from Pi to a Laptop? Currently I'm using plain text files to save the data. Also, it would be nice, if the measurements aren't interrupted and if I could read the data in real time. In terms of hardware, I have a Bluetooth and a Wifi Dongle for my Pi. What would you suggest?
Internet sharing without internet. Either direction should work.
The basic idea is that sometimes users connect their laptop to the internet via cable, then use wifi to share that internet connection to other devices. What's actually happening is the laptop is serving the functions of a router, i.e. creating a private network. In this case you set the pi up to watch for specific network (the laptop) and it when it finds it it joins. When both are on the local traveling network that you created you just ssh to the pi like you normally would.
next idea, Same thing is reverse. Set the pi up to be a router and connect the laptop to it. This may actually be better than above because it requires fewer if any changes to the laptop, it's still just connection to a network, this time a network created by the pi.
Any even better idea, but requires you to buy one more piece of hardware, is a travel router. (one you have one of these you will never want travel without one again.) The concept is simple a shirt pocket sized router for the hotel room. They used to always require a cable to get the internet, but created a nice local wifi network. Now there are models that get the internet via WIFI and create the local network on another channel. The huge advantage is neither of your devices need any special reconfiguration, you just join the travel routers SSID like you would any other wireless network. No internet connection no problem, you are just after the creation of the local network.
Some time ago, I installed hostapd on the Arch Linux distribution. This allows your rPi to be a wireless access point. Your wifi dongle must have the AP ability, not all of them do. I used a TPLink TL-WN821N, as I recall, a rev B. kinda large, but has great range and speed. Here's a link to the Arch Linux Wiki: https://wiki.archlinux.org/index.php/Software_access_point
Then, using lighttpd, build a web page and update via PHP. Kinda busy setup, but works marvy if you want to spend the time.
On your laptop, you can connect to the rPi access point and you will have your very own private wireless intranet.
I have not tried with raspbian or others, but what you intend sounds very do-able.