Use this technique to 'float' two tables next to each other using the html align attribute.
If you want something to be 100% width though, the only way to guarantee it is to go with a single column with width="100%"
. As Gmail doesn't accept media queries, there is no way to do both float/align and full width.
Note - In my example I've used 320px as that is the width of most Android phones, so when the tables stack, it will appear full width.
Edit: here is a full email example:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><title></title>
<style type="text/css">
/* Client-specific Styles - last updated 18 July 2013 */
#outlook a {padding:0;}
body{width:100% !important; -webkit-text-size-adjust:100%; -ms-text-size-adjust:100%; margin:0; padding:0;} /* force default font sizes */
.ExternalClass {width:100%;} .ExternalClass, .ExternalClass p, .ExternalClass span, .ExternalClass font, .ExternalClass td, .ExternalClass div {line-height: 100%;} /* Hotmail */
a[href^="tel"], a[href^="sms"] { text-decoration: default; color: #000001 !important; pointer-events: auto; cursor: default;}
table td {border-collapse: collapse;}
.msoFix {
mso-table-lspace:-1pt;
mso-table-rspace:-1pt;
}
</style>
</head>
<body style="margin: 0px; padding: 0px; background-color: #FFFFFF;" bgcolor="#FFFFFF">
<table width="100%" border="0" align="center" cellpadding="0" cellspacing="0">
<tr>
<td align="center">
<div style="max-width:640px !important;">
<table class="msoFix" width="320" cellpadding="0" cellspacing="0" align="left" bgcolor="#CCCCCC">
<tr>
<td width="15" bgcolor="454545"> </td>
<td width="290" bgcolor="454545" style="padding: 0px;"> <br>table 1<br>...<br>
</td>
<td width="15" bgcolor="454545"> </td>
</tr>
</table>
<table class="msoFix" width="320" cellpadding="0" cellspacing="0" align="left" bgcolor="#EEEEEE">
<tr>
<td width="15" bgcolor="959595"> </td>
<td width="290" bgcolor="959595" style="padding: 0px;"> <br>table 2<br>...<br>
</td>
<td width="15" bgcolor="959595"> </td>
</tr>
</table>
</div>
</td>
</tr>
</table>
</body></html>