Update, May 26, 2021: Buonos are still my favorite end node platform, but they are getting harder to find. I had to pare down the shopping links.
To build nodes, I've also used a Prototype Shield for Arduino. More on these below.
Building a node requires the ability to make needed connections between parts & signals. Some connections are more plentiful. For example, an Arduino compatible typically has 3 GND sockets. An Arduino shield on top can add 5 more GND sockets.
For the sake of items like our RFM69 radio, we need multiple 3.3 volt sources. However, even when a Buono Uno compatible is switched to 3.3 volt mode, it only has one dedicated 3.3 volt socket.
Sometimes we need to connect more than two locations. For example, we need to connect a DS18 sensor's data pin to both a digital pin (D3) & via a pull-up resistor to 3.3 volts.
One way to gain more 3.3 volt connections is to configure an Arduino digital pin to output 3.3 volts. the choose_nodes sketch has an example:
#define DS18power 5 // D5 powers DS18B sensor
digitalWrite(DS18power, HIGH); // ... power DS18 sensor
This method is OK when a pin is available & we only need one or two extras. This way makes more to keep track of & our pins may already be committed.
Starting at this post, I described another way to multiply possible connections. It's an involved "surgery" on an Arduino prototyping shield to add more 3.3 volt locations & other means to make needed connections. I've made & used several of these, but this approach is time consuming.
These approaches are still valid, but have issues & limitations.
^^ As with this Irrigation Automation Node, I've successfully used another easier method, an as-is Arduino Shield & a small solderless breadboard nestled on top of the shield. One can still use shield sockets that don't need altering (like D10-D13 for the RFM69 radio). Insulated solid wire jumpers can make connections between needed shield sockets (3.3 volt, GND, etc) & a strip of solderless breadboard sockets.
Solid wire jumpers between Arduino/shield sockets to the breadboard also help hold the solderless breadboard in place on the shield. Moreover the breadboards may have double-sided tape to adhere them to the shield.
These bread boards have thirty-four 5-socket strips. So at each strip, we can connect up to 5 things together. We can also connect strips to each other. The breadboard sockets are tighter than the shield sockets so they are more secure for smaller leads as on transistors & resistors, but they still work for larger leads as on Dupont cable pins.
Like this ^^, we can currently buy combo packs of the prototyping shield plus the mini solderless breadboard: