Speedlites offer a large variety of power, portability, and consistent light output. I always have at least a couple in my kit, along with a wireless triggering system. The benefits that this setup offers outweigh the limitations of battery-life and possible issues with weather sealing. Those limitations are fairly easy to overcome by carrying some extra batteries and plastic bags for inclement weather.
Diffusing the light that your flash produces is critical to achieving a soft, desirable light for your scene. Most Canon Speedlites have a built-in diffusion screen and bounce card, which can provide a small amount of extra control over how your light behaves. However, I recommend starting with a small softbox that attaches directly to your flash unit. These types of modifiers typically cost around $20, and fold flat for easy storage when carrying them in your kit. They come in a variety of sizes and quality of materials, depending on the brand that you go with.
When I need to spread my light over a larger area than what a small softbox can offer, I utilize a larger softbox or reflective umbrella. These types of modifiers allow a much wider spread of light, and softer gradation of shadow over the subject. Conversely, if I want to concentrate my light into a particular area, I would use a honeycomb grid. This device acts as a way to narrow your flash into a single beam (versus a cone) and results in a spotlight effect. This can be great for highlighting one particular element or avoiding light spill into unwanted areas in your scene.
If you’re looking for makeshift ways to achieve the same dynamics of your flash, there are lots of household items that can help you achieve similar effects. A white food storage container (like the plastic container that Chinese food often comes in) makes a great softbox in a pinch. Just cut a hole for your flash to fit through on the bottom, and place a paper towel on the underside of the lid. If you want to go bigger, try doing the same thing with a plastic dishwashing tub from a general store, or a styrofoam cooler for an even larger spread. Another DIY modifier for this type of light is a paper lantern, but I’ve found that this method is too fragile (as they break fairly easily, due to the thin paper).