Now that we have seen how artists interpreted outdoor clothes in the early 1870s, lets take a look at some real outfits that might have been worn to picnics in 1871.
For the ladies, dresses would most likely be of plain, unpatterned fabric, trimmed with fringe, braid, and bias strips in either matching or contrasting tones. The silhouette and would demonstrate the change from the back heavy, oval hoops of the 1860s to the bustled 1870s silhouette. Fabrics would be of wool, silk, or cotton depending on the weather, and how fashionable and up-to-date the wearer was.
Four silk dresses:

Outdoor dresses, 1867-1871, Metropolitan Museum of Art
If the weather was relatively cool, very fashionable ladies might wear highly trimmed silk dresses, such as this one:

Dress, 1868-69, UK, Collection of the V&A
The design and trim of this dress are very similar to the one shown in Monet’s painting on Monday.
In warmer weather, light cotton dresses similar to the ones shown in Monet’s Women in the Garden would be ideal.

Day dress, 1869, UK, Collection of the V&A
These dresses are quite easily soiled and torn, but also easily put together. They seem to have been extremely common in the late 1860s and early 1870s, with the bustled effect becoming more and more pronounced as the years went on.
The more practical minded were likely to wear much simpler dresses, such as these:

Afternoon dress, European, 1865-1871, Collection of the Metropolitan Museum of Art

Dress, 1870, American, Collection of the Metropolitan Museum of Art
Older women could wear looser fashions:

Dress, UK, ca 1870, Collection of the V&A
If you wanted to be practical, and fashionable, a wool dress with bright trimmings, such as this one, would be ideal:

Dress, about 1868, American, Boston Museum of Fine Art
Do click on the image to be taken to the museum’s page, because the back view of this dress is lovely.
All of these dresses would be worn with hats, gloves, parasols, and various wraps and shawls: accessories images coming tomorrow!
And what would men wear? Ummmm….the stuff you see in paintings and drawings. Not many examples of their extent garments were preserved.