base.tpl

{{define "base"}}
Header, whatever....

{{template "content" .}}

Footer... whatever!
{{end}}

main.go

package main

import(
	"fmt"
	"os"
	"errors"
	"html/template"
)

// NOTE: This is a Variadic Function.
func XTPL(templatefiles ...string) (*template.Template, error) {
	templates, err := template.New("").ParseFiles(templatefiles ...)

	if err != nil {
		return nil, err
	}

	tpl := templates.Lookup("base.tmpl")
	if tpl == nil {
		return tpl, errors.New("Base template not found.")
	}

	return tpl, nil
}

type MyData struct {
	Things		[]string
}

func main(){

	tpl1, err1 := XTPL(
		"page1.tmpl",
		"base.tmpl",
	)
	fmt.Println("template err?", err1)
	tpl1.ExecuteTemplate(os.Stdout, "base", nil)


	var stuff MyData
	stuff.Things = append(stuff.Things, "Element1", "Element2", "Element3")

	tpl2, err2 := XTPL(
		"page2.tmpl",
		"base.tmpl",
	)
	fmt.Println("template err?", err2)
	tpl2.ExecuteTemplate(os.Stdout, "base", stuff)

	var stuff2 []interface{}
	stuff2 = append(stuff2, "Element1x", "Element2x", "Element3x", 1, 2, 3)

	tpl3, err3 := XTPL(
		"page3.tmpl",
		"base.tmpl",
	)
	fmt.Println("template err?", err3)
	tpl3.ExecuteTemplate(os.Stdout, "base", stuff2)
}

page1.tpl

{{define "content"}}
WHATEVER! :D
{{end}}

page2.tpl

{{define "content"}}
	WHATEVER2! :D
	{{range .Things}}
	{{.}}
	{{end}}
{{end}}

page3.tpl

{{define "content"}}
	WHATEVER2! :D
	{{range .}}
	{{.}}
	{{end}}
{{end}}