That's an excellent and practical question! Dealing with uneven ground is a common headache in urban settings. From my experience, the best base isn't a one-size-fits-all solution, but rather one that prioritizes stability, accessibility, and durability.
For a truly effective setup, I'd recommend looking for a trash can with a built-in adjustable leveling base. These are fantastic. Think of them like the adjustable feet on a washing machine. Each corner can be screwed up or down independently to compensate for slopes, cracks, and dips in the pavement. This ensures the bin stands upright, preventing it from rocking or, worse, tipping over and spilling litter.
If a custom adjustable base isn't an option, a heavy, weighted flat plate base is a strong alternative. A wide, solid platform made of concrete composite or heavy-duty plastic adds significant low-center gravity. The wide footprint distributes the weight and prevents the bin from sinking into soft soil or gravel. It's less precise than adjustable feet but offers great general stability on mildly uneven surfaces.
For permanent installations on rough terrain, a poured concrete pad is the gold standard. You can form and level a small concrete slab to create a perfectly flat and stable foundation. This is more labor-intensive but provides unmatched permanence and can be sized to accommodate multiple bins.
A few pro tips: Always secure the bin to its base with bolts or sturdy straps, especially in windy areas. Avoid simple spike or stake bases for hard surfaces like cobblestone—they won't anchor properly. For areas with frequent foot traffic, ensure the base solution doesn't create a tripping hazard; a flush, low-profile design is ideal.
Ultimately, the "best" base minimizes maintenance, keeps the area clean, and ensures the trash can serves its purpose reliably, no matter the bumps in the road.