Find what fraction of the original money each purchase represents.

\$\begin{aligned}
\text{After sandwich (30\%)} &: 70\% \text{ remaining}
\\
\text{Juice: 40\% of remainder} &= 0.40 \times 70\% = 28\% \text{ of original}
\\
\text{Total spent} &= 30\% + 28\% = 58\%
\\
\text{Money left} &= 100\% - 58\% = 42\% = \$12.60
\\
\text{Original} &= \$12.60 \div 0.42 = \$30
\end{aligned}\$

Final Answer: \$30